Introduction to Computer
Definition :
Computer is fast and accurate electronic device capable of accepting data, store it, process it as predefined stored instructions and give the result.
Technically, a computer is a programmable machine. This means it can execute a programmed list of instructions and respond to new instructions that it is given. Today, however, the term is most often used to refer to the desktop and laptop computers that most people use. When referring to a desktop model, the term "computer" refer to everything together the monitor, keyboard, and mouse as the computer. If you want to be really technical, the box that holds the computer is called the "system unit."
Some of the major parts of a personal computer (or PC) include the motherboard, CPU, memory (or RAM), hard drive, and video card. While personal computers are by far the most common type of computers today, there are several other types of computers. For example, a "minicomputer" is a powerful computer that can support many users at once. A "mainframe" is a large, high-powered computer that can perform billions of calculations from multiple sources at one time. Finally, a "supercomputer" is a machine that can process billions of instructions a second and is used to calculate extremely complex calculations.
Diagram showing elements of Computer system and Logical connection Input Unit : Inserts data and instruction to main memory . Main Memory : Holds input data, instruction and processed result . Auxiliary Memory : Supports main memory and backing storage . Control Unit : Interrupt stored instruction in sequence . Issuing commands to all element of computer. ALU : Perform Arithmetic and Logical operations . Output Unit : Show/produce result of the processed information . Input Devices:
Any machine that feeds data into a computer. For example, a keyboard is an input device. Input devices establish the communication link between the user and computer system. There are various types of input devices. Input devices other than the keyboard are sometimes called alternate input devices. Mice, trackballs and light pens are all alternate input devices. Input Unit Keyboard Mouse Scanner Joystick Processing/System Unit
Keyboard Mouse Joystick Track Ball Light pen Touch screen Optical mark reader Optical character reader Magnetic ink character recognition Bar code reader Punch card & card reader Paper tape & paper tape reader Scanner
Keyboard:
The set of typewriter-like keys that enables you to enter data into a computer. Computer keyboards are similar to electric-typewriter keyboards but contain additional keys. The keys on computer keyboards are often classified as follows:
Alphanumeric keys -- letters and numbers
Punctuation keys -- comma, period, semicolon, and so on.
Special keys -- function keys, control keys, arrow keys, Caps Lock key, and so on.
The standard layout of letters, numbers, and punctuation is known as a QWERTY keyboard because the first six keys on the top row of letters spell QWERTY. The QWERTY keyboard was designed in the 1800s for mechanical typewriters and was actually designed to slow typists down to avoid jamming the keys. Another keyboard design, which has letters positioned for speed typing, is the Dvorak keyboard. The Dvorak keyboard was designed with the most common consonants on one side of the middle or home row and the vowels on the other side so that typing tends to alternate key strokes back and forth between hands. Although the Dvorak keyboard has never been widely used, it has adherents.
There is no standard computer keyboard, although many manufacturers imitate the keyboards of PCs. There are actually three different PC keyboards: the original PC keyboard, with 84 keys; the AT keyboard, also with 84 keys; and the enhanced keyboard, with 101 or more keys. The three differ somewhat in the placement of function keys, the Control key, the Return key, and the Shift keys.
In addition to these keys, IBM keyboards contain the following keys: Page Up, Page Down, Home, End, Insert, Pause, Num Lock, Scroll Lock, Break, Caps Lock, Print Screen.
There are several different types of keyboards for the Apple Macintosh. All of them are called ADB keyboards because they connect to the Apple Desktop bus (ADB). The two main varieties of Macintosh keyboards are the standard keyboard and the extended keyboard, which has 15 additional special-function keys.
A circuit called Keyboard_encoder detects key press on keyboard. It generates binary code & is send to the system unit. Keyboards may be wired or wireless but they always communicate with the computer via PS/2 or USB connections, usually located on the motherboard. Even though the keyboard sits outside the main computer housing, it is an essential part of the complete system. Mouse:
In computing, a mouse is a pointing device that functions by detecting two-dimensional motion relative to its supporting surface. Physically, a mouse consists of an object held under one of the user's hands, with one or more buttons. It sometimes features other elements, such as "wheels", which allow the user to perform various system-dependent operations, or extra buttons or features that can add more control or dimensional input. The mouse's motion typically translates into the motion of a pointer on a display, which allows for fine control of a graphical user interface.
Independently, Douglas Engelbart at the Stanford Research Institute invented the first mouse prototype in 1963,[4] with the assistance of his colleague Bill English. They named the device the mouse as early models had a cord attached to the rear part of the device looking like a tail and generally resembling the common mouse and pioneered by Xerox in the 1970s, the mouse is one of the great breakthroughs in computer world because it frees the user to a large extent from using the keyboard. In particular, the mouse is important for graphical user interfaces because you can simply point to options and objects and click a mouse button. Such applications are often called point-and-click programs. The mouse is also useful for graphics programs that allow you to draw pictures by using the mouse like a pen, pencil, or paintbrush. There are three basic types of mice:
1. Mechanical: Has a rubber or metal ball on its underside that can roll in all directions. Mechanical sensors within the mouse detect the direction the ball is rolling and move the screen pointer accordingly.
2. Optomechanical: Same as a mechanical mouse, but uses optical sensors to detect motion of the ball.
3. Optical: Optical mice make use of one or more light-emitting diodes (LEDs) and an imaging array of photodiodes to detect movement relative to the underlying surface, rather than internal moving parts as does a mechanical mouse. A laser mouse is an optical mouse that uses coherent (laser) light.
Mice connect to PCs in one of several ways:
1. Serial mice connect directly to an RS-232C serial port or a PS/2 port. This is the simplest type of connection.
2. USB mice.
Cordless mice aren't physically connected at all. Instead they rely on infrared or radio waves to communicate with the computer. Cordless mice are more expensive than both serial and USB mice, but they do eliminate the cord, which can sometimes get in the way. Scanner :
In computing, an image scanner—often abbreviated to just scanner—is a device that optically scans images, printed text, handwriting, or an object, and converts it to a digital image. Common examples found in offices are variations of the desktop (or flatbed) scanner where the document is placed on a glass window for scanning. A scanner works
by digitizing an image -- dividing it into a grid of boxes and representing each box with either a zero or a one, depending on whether the box is filled in. (For color and gray scaling, the same principle applies, but each box is then represented by up to 24 bits.) The resulting matrix of bits, called a bit map, can then be stored in a file, displayed on a screen, and manipulated by programs.
Optical scanners do not distinguish text from illustrations; they represent all images as bit maps. Therefore, you cannot directly edit text that has been scanned. To edit text read by an optical scanner, you need an optical character recognition (OCR ) system to translate the image into ASCII characters. Most optical scanners sold today come with OCR packages.. Trackball:
A trackball is a pointing device consisting of a ball held by a socket containing sensors to detect a rotation of the ball about two axes—like an upside-down mouse with an exposed protruding ball. The user rolls the ball with the thumb, fingers, or the palm of the hand to move a pointer. Compared with a mouse, a trackball has no limits on effective travel; at times, a mouse can reach an edge of its working area while the operator still wishes to move the screen pointer farther. With a trackball, the operator just continues rolling.
Large trackballs are common on CAD workstations for easy precision. Before the advent of the touchpad, small trackballs were common on portable computers, where there may be no desk space on which to run a mouse. Some small thumb balls clip onto the side of the keyboard and have integral buttons with the same function as mouse buttons. The trackball was invented by Tom Cranston and Fred Longstaff as part of the Royal Canadian Navy's DATAR system in 1952, eleven years before the mouse was invented. This first trackball used a Canadian five-pin bowling ball. Joystick:
A joystick is an input device consisting of a stick that pivots on a base and reports its angle or direction to the device it is controlling. Potentiometers within the base translate X-Y position information into voltage which can then be encoded in binary for input to digital system. They often have supplementary switches on them to control.
Joysticks are often used to control video games, and usually have one or more push-buttons whose state can also be read by the computer. A popular variation of the joystick used on modern video game consoles is the analog stick. Joysticks are also used for controlling machines such as cranes, trucks, underwater unmanned vehicles, wheelchairs, surveillance cameras etc.. Small finger-operated joysticks have been adopted as input devices for smaller electronic equipment such as mobile phones. Light pen:
A light pen is a computer input device in the form of a light-sensitive stick used in conjunction with a computer's CRT TV set or monitor. It allows the user to point to displayed objects, or draw on the screen, in a similar way to a touch screen but with greater positional accuracy. It was long thought that a light pen can work with any CRT-based display, but not with LCD screens, projectors and other display devices. A light pen works by sensing the sudden small change in brightness of a point on the screen when the electron gun refreshes that spot. By noting exactly where the scanning has reached at that moment, the X,Y position of the pen can be resolved. This is usually achieved by the light pen causing an interrupt, at which point the scan position can be read from a special register, or computed from a counter or timer. The pen position is updated on every refresh of the screen
The first light pen was created around 1952 as part of the Whirlwind project at Massachusetts Institute of Technology.
A Touchpad (or Trackpad) is a pointing device featuring a tactile sensor, a specialized surface that can translate the motion and position of a user's fingers to a relative position on screen. Touchpad is a common feature of laptop computers, and are also used as a substitute for a mouse where desk space is scarce. Because they vary in size, they can also be found on personal digital assistants (PDAs) and some portable media players. Wireless touchpads are also available as detached accessories. Optical character recognition:- usually abbreviated to OCR, is the mechanical or electronic translation of scanned images of handwritten, typewritten or printed text into machine-encoded text. It is widely used to convert books and documents into electronic files, to computerize a record-keeping system in an office, or to publish the text on a website. OCR makes it possible to edit the text, search for a word or phrase, store it more compactly, display or print a copy free of scanning artifacts, and apply techniques such as machine translation, text-to-speech and text mining to it. OCR is a field of research in pattern recognition, artificial intelligence and computer vision. Magnetic Ink Character Recognition, or MICR, is a character recognition technology used primarily by the banking industry to facilitate the processing of cheques and makes up the routing number and account number at the bottom of a check. The technology allows computers to read information (such as account numbers) off printed documents. Unlike barcodes or similar technologies, however, MICR codes can be easily read by humans.
MICR characters are printed in special typefaces with a magnetic ink or toner, usually containing iron oxide. As a machine decodes the MICR text, it first magnetizes the characters in the plane of the paper. Then the characters are
passed over a MICR read head, a device similar to the playback head of a tape recorder. As each character passes over the head it produces a unique waveform that can be easily identified by the system.
The use of magnetic printing allows the characters to be read reliably even if they have been overprinted or obscured by other marks, such as cancellation stamps and signature. The error rate for the magnetic scanning of a typical check is smaller than with optical character recognition systems.
A Barcode Reader (or Barcode Scanner) is an electronic device for reading printed barcodes. Like a flatbed scanner, it consists of a light source, a lens and a light sensor translating optical impulses into electrical ones. Additionally, nearly all barcode readers contain decoder circuitry analyzing the barcode's image data provided by the sensor and sending the barcode's content to the scanner's output port. Central Processing Unit (CPU)
The central processing unit (CPU) is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The form, design and implementation of CPUs have changed dramatically since the earliest examples, but their fundamental operation remains much the same.
On large machines, CPUs require one or more printed circuit boards. On personal computers and small workstations, the CPU is housed in a single silicon chip called a microprocessor. Since the 1970s the microprocessor class of CPUs has almost completely overtaken all other CPU implementations. Modern CPUs are large scale integrated circuits in packages typically less than four centimeters square, with hundreds of connecting pins.
Two typical components of a CPU are the arithmetic logic unit (ALU), which performs arithmetic and logical operations, and the control unit(CU), which extracts instructions from memory and decodes and executes them, calling on the ALU when necessary. Control Unit : The control unit of the CPU contains circuitry that uses electrical signals to direct the entire computer system to carry out stored program instructions. The control unit does not execute program instructions; rather, it directs other parts of the system to do so. The control unit must communicate with both the arithmetic/logic unit and memory The control unit is one of the most important parts of a microprocessor for the reason that it is in charge of the entire process, that is the machine cycle. The CPU deals with each instruction it is given in a series of steps. Each step is repeated for each instruction. This series of steps is called the machine cycle. It involves:
fetching an instruction from memory;
decoding the instruction;
transferring the data;
executing the instruction.
The control unit makes sure that all of those actions are carried out. It also manages all the other components on the CPU. Arithmetic and Logic Unit :
In computing, an arithmetic logic unit (ALU) is a digital circuit that performs arithmetic and logical operations. The ALU is a fundamental building block of the central processing unit of a computer, and even the simplest microprocessors contain one for purposes such as maintaining timers. It contains circuit to perform the arithmetical operation on numbers and logical tests for equality, greater then and less then between operations. Final results are transferred to memory. Data Storage Device
A data storage device is a device for recording (storing) information (data). Recording can be done using virtually any form of energy, spanning from manual muscle power in handwriting, to acoustic vibrations in phonographic recording, to electromagnetic energy modulating magnetic tape and optical discs.
A storage device may hold information, process information, or both. A device that only holds information is a recording medium. Devices that process information (data storage equipment) may either access a separate portable (removable) recording medium or a permanent component to store and retrieve information.
Electronic data storage is storage which requires electrical power to store and retrieve that data. Electromagnetic data may be stored in either an analog or digital format on a variety of media. This type of data is considered to be electronically encoded data, whether or not it is electronically stored in a semiconductor device, for it is certain that a semiconductor device was used to record it on its medium. Most electronically processed data storage media (including some forms of computer data storage) are considered permanent (non-volatile) storage, that is, the data will remain stored when power is removed from the device. In contrast, most electronically stored information within most types of semiconductor (computer chips) microcircuits are volatile memory, for it vanishes if power is removed.
Primary or Main Memory: Primary storage (or main memory or internal memory), often referred to simply as memory, is the only one directly accessible to the CPU. The CPU continuously reads instructions stored there and executes them as required. Any data actively operated on is also stored there in uniform manner. Main memory is divided into two parts : RAM (Random Access Memory) and ROM (Read Only Memory) RAM (Random Access Memory) Random Access Memory is responsible for storing the instruction and data that the computer is using at that present moment in time. It is volatile memory, which means item stored in RAM are lost when the power to the computer is turned off. There are mainly two types of RAM : SRAM (Static Random Access Memory)
Faster and more reliable than any form of DRAM. The static refers to the fact that it does not have to be re-energized as often as DRAM. The access time is 10-100ns and does not need refresh cycles. a bit of data is stored using the state of a flip-flop. This form of RAM is more expensive to produce, but is generally faster and requires less power. DRAM (Dynamic Random Access Memory ) DRAM stores a bit of data using a transistor and capacitor pair, which together comprise a memory cell. The capacitor holds a high or low charge (1 or 0, respectively), and the transistor acts as a switch that lets the control circuitry on the chip read the capacitor's state of charge or change it. Due to leakage the capacitor discharges gradually and memory cell loses the information. Therefore to preserve the information the memory has to be refreshed periodically. It is popular as high density and low price. Access time is 40-70 ns or less. As this form of memory is less expensive to produce than static RAM, it is the predominant form of computer memory used in modern computers. The other types of DRAM is Synchronous DRAM(SDRAM) and Rambus DRAM(RDRDM) which is much faster than DRAM. ROM (Read Only Memory)
Read-only memory (ROM) is a class of storage medium used in computers and other electronic devices. Data stored in ROM cannot be modified, or can be modified only slowly or with difficulty, so it is mainly used to distribute firmware (software that is very closely tied to specific hardware, and unlikely to need frequent updates). ROM is a permanent type memory. Its contents are not lost when power supply goes off. Its contents are decided by manufacturer and written at the time of manufacture. Generally the ROM of microcomputer contains system programs for handling the operating system. The user programmable ROMs are also available in the following types. Programmable Read-Only Memory (PROM), or One-Time Programmable ROM (OTP), can be written to or programmed via a special device called a PROM programmer. Typically, this device uses high voltages to permanently destroy or create internal links (fuses or antifuses) within the chip. Consequently, a PROM can only be programmed once. Erasable Programmable Read-Only Memory (EPROM) can be erased by exposure to strong ultraviolet light (typically for 10 minutes or longer), then rewritten with a process that again needs higher than usual voltage applied. Repeated exposure to UV light will eventually wear out an EPROM, but the staying power of most EPROM chips exceeds 1000 cycles of erasing and reprogramming. EPROM chip packages can often be identified by the prominent quartz "window" which allows UV light to enter. After programming, the window is typically covered with a label to prevent accidental erasure. Some EPROM chips are factory-erased before they are packaged, and include no window; these are effectively PROM. Electrically Erasable Programmable Read-Only Memory (EEPROM) is based on a similar semiconductor structure to EPROM, but allows its entire contents (or selected banks) to be electrically erased, then rewritten electrically, so that they need not be removed from the computer (or camera, MP3 player, etc.). Writing or flashing an EEPROM is much slower (milliseconds per bit) than reading from a ROM or writing to a RAM (nanoseconds in both cases). Electrically Alterable Read-Only Memory (EAROM) is a type of EEPROM that can be modified one bit at a time. Writing is a very slow process and again needs higher voltage (usually around 12 V) than is used for read access. EAROMs are intended for applications that require infrequent and only partial rewriting. EAROM may be used as non-volatile storage for critical system setup information; in many applications, EAROM has been supplanted by CMOS RAM supplied by mains power and backed-up with a lithium battery. Flash memory (or simply flash) is a modern type of EEPROM invented in 1984. Flash memory can be erased and rewritten faster than ordinary EEPROM, and newer designs feature very high endurance (exceeding 1,000,000 cycles). Modern NAND flash makes efficient use of silicon chip area, resulting in individual ICs with a capacity as high as 32 GB as of 2007; this feature, along with its endurance and physical durability, has allowed NAND flash to replace magnetic in some applications (such as USB flash drives). Flash
memory is sometimes called flash ROM or flash EEPROM when used as a replacement for older ROM types, but not in applications that take advantage of its ability to be modified quickly and frequently. By applying write protection, some types of reprogrammable ROMs may temporarily become read-only memory CACHE MEMORY: This is a small amount of high speed memory that lies between the CPU and main memory. The memory contains frequently required data and instructions. When CPU needs to access any information or data it first checks if the data is available in the cache memory. Only if needed data is unavailable with cache memory it will make a trip to the main memory. Usually systems come with 256 KB to 4MB of cache memory.
A CPU cache is a cache used by the central processing unit of a computer to reduce the average time to access memory. The cache is a smaller, faster memory which stores copies of the data from the most frequently used main memory locations. As long as most memory accesses are cached memory locations, the average latency (delays in transmitting data between the CPU and RAM) of memory accesses will be closer to the cache latency than to the latency of main memory Most modern computers have 2 types or Layers of Cache Level 1 (L1)and Level 2 (L2). L1 Cache is built directly into the processor chip, faster and small capacity than L2 Cache. L2 Cache (high speed SRAM) is larger in capacity, slower than L1 Cache and lies between CPU and Main Memory. Multi-level caches generally operate by checking the smallest Level 1 (L1) cache first; if it hits, the processor proceeds at high speed. If the smaller cache misses, the next larger cache (L2) is checked, and so on, before external memory is checked. Secondary or Auxiliary Memory: Secondary storage (also known as external memory or auxiliary storage), differs from primary storage in that it is not directly accessible by the CPU. The computer usually uses its input/output channels to access secondary storage and transfers the desired data using intermediate area in primary storage. Secondary storage does not lose the data when the device is powered down—it is non-volatile. Per unit, it is typically also two orders of magnitude less expensive than primary storage. Consequently, modern computer systems typically have two orders of magnitude more secondary storage than primary storage and data are kept for a longer time there.
In modern computers, hard disk drives are usually used as secondary storage. The time taken to access a given byte of information stored on a hard disk is typically a few thousandths of a second, or milliseconds. By contrast, the time taken to access a given byte of information stored in random access memory is measured in billionths of a second, or nanoseconds. This illustrates the significant access-time difference which distinguishes solid-state memory from rotating magnetic storage devices: hard disks are typically about a million times slower than memory. Rotating optical storage devices, such as CD and DVD drives, have even longer access times. With disk drives, once the disk read/write head reaches the proper placement and the data of interest rotates under it, subsequent data on the track are very fast to access. As a result, in order to hide the initial seek time and rotational latency, data are transferred to and from disks in large contiguous blocks.
Some other examples of secondary storage technologies are: flash memory (e.g. USB flash drives ), floppy disks, magnetic tape, paper tape, punched cards, standalone RAM disks, and Iomega Zip drives. Hard disks :
A hard disk drive (HDD; also hard drive, hard disk, or disk drive) is a device for storing and retrieving digital information, primarily computer data. It consists of one or more rigid (hence "hard") rapidly rotating discs (often referred to as platters), coated with magnetic material and with magnetic heads arranged to write data to the surfaces and read it from them. Hard drives are classified as non-volatile, random access, digital, magnetic, data storage devices. Introduced by IBM in 1956, hard disk drives have decreased in cost and physical size over the years while dramatically increasing in capacity and speed. Hard disk drives have been the dominant device for secondary storage of data in general purpose computers since the early 1960s. They have maintained this position because advances in their recording capacity, cost, reliability, and speed have kept pace with the requirements for secondary storage As disk pack is sealed containers are dust free and they allow very high speed usually 4200rpm-15000rpm. A hard disk may have more than 10,000 tracks per surface bit density 15,00 bits per inch. Data transfer rate 33.3 to 160MB per second. The hard disk come in 2.5 inch, 3.5 inch and 5.25 inch diameter. Hard disk controller are used to interface hard disk to a processor. Floppy disk:
A floppy disk is a disk storage medium composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles. They are read and written by a floppy disk drive (FDD). Floppy disks, initially as 8-inch (200 mm) media and later in 5.25-inch (133 mm) and 3.5-inch (89 mm) sizes, were a ubiquitous form of data storage and exchange from the mid-1970s well into the first decade of the 21st century.
By 2010, computer motherboards were rarely manufactured with floppy drive support; 3 1⁄2" floppies could be used with an external USB drive, but 5 1⁄4", 8", and non-standard drives could only be handled by old equipment.
While floppy disk drives still have some limited uses, they have been superseded by data storage methods with much greater capacity, such as USB flash drives, portable external hard disk drives, optical discs, memory cards, and computer networks. Optical Storage Disk: It was developed from video disk technology during early 1980s
In computing and optical disc recording technologies, an optical disc is a flat, usually circular disc which encodes binary data (bits) in the form of pits (binary value of 0 or off, due to lack of reflection when read) and lands (binary value of 1 or on, due to a reflection when read) on a special material (often aluminium on one of its flat surfaces. The encoding material sits atop a thicker substrate (usually polycarbonate) which makes up the bulk of the disc and forms a dust defocusing layer. The encoding pattern follows a continuous, spiral path covering the entire disc surface and extending from the innermost track to the outermost track. The data is stored on the disc with a laser or stamping machine, and can be accessed when the data path is illuminated with a laser diode in an optical disc drive which spins the disc at speeds of about 200 to 4000RPM or more, depending on the drive type, disc format, and the distance of the read head from the center of the disc (inner tracks are read at a faster disc speed). The pits or bumps distort the reflected laser light, hence most optical discs (except the black discs of the original PlayStation video game console) characteristically have an shining appearance created by the grooves of the reflective layer. The reverse side of an optical disc usually has a printed label, generally made of paper but sometimes printed or stamped onto the disc itself. This side of the disc contains the actual data and is typically coated with a transparent material, usually polish. Unlike the 3½-inch floppy disk, most optical discs do not have an integrated protective casing and are therefore susceptible to data transfer problems due to scratches, fingerprints, and other environmental problems.
Optical discs are usually between 7.6 and 30 cm (3 to 12 in) in diameter, with 12 cm (4.75 in) being the most common size. A typical disc is about 1.2 mm (0.05 in) thick, while the track pitch (distance from the center of one track to the center of the next) is typically 1.6 μm.
An optical disc is designed to support one of three recording types: read-only (e.g.: CD and CD-ROM), recordable (write-once, e.g. CD-R), or re-recordable (rewritable, e.g. CD-RW). Write-once optical discs commonly have an organic dye recording layer between the substrate and the reflective layer. Rewritable discs typically contain an alloy recording layer composed of a phase change material, most often AgInSbTe, an alloy of silver, indium, antimony and tellurium.
Optical discs are most commonly used for storing music (e.g. for use in a CD player), video (e.g. for use in a DVD (Digital Versatile Disk) player), or data and programs for personal computers (PC). The Optical Storage Technology Association (OSTA) promotes standardized optical storage formats. Although optical discs are more durable than earlier audio-visual and data storage formats, they are susceptible to environmental and daily-use damage. Libraries and archives enact optical media preservation procedures to ensure continued usability in the computer's optical disc drive or corresponding disc player
A USB flash drive : is a data storage device that consists of flash memory with an integrated Universal Serial Bus (USB) interface. USB flash drives are typically removable and rewritable, and physically much smaller than a floppy disk. Most weigh less than 30 g. As of September 2011 drives of 256 gigabytes (GB) are available, and storage capacities as large as 2 terabytes (TB) are planned, with steady improvements in size and price per capacity expected. Some allow up to 100,000 write/erase cycles (depending on the exact type of memory chip used) and 10 years shelf storage time.
USB flash drives are often used for the same purposes for which floppy disks or CD-ROMs were used. They are smaller, faster, have thousands of times more capacity, and are more durable and reliable because they have no moving parts. Until approximately 2005, most desktop and laptop computers were supplied with floppy disk drives, but floppy disk drives have been dumped in favor of USB ports.
A flash drive consists of a small printed circuit board carrying the circuit elements and a USB connector, insulated electrically and protected inside a plastic, metal, or rubberized case which can be carried in a pocket or on a key chain, for example. The USB connector may be protected by a removable cap or by retracting into the body of the drive, although it is not likely to be damaged if unprotected. Most flash drives use a standard type-A USB connection allowing plugging into a port on a personal computer, but drives for other interfaces also exist.
USB flash drives draw power from the computer via external USB connection. Some devices combine the functionality of a digital audio player with USB flash storage; they require a battery only when used to play music. MICROFILM: It is a high resolution film on which photographic records of documents or other materials are kept in reduced size. A sheet of microfilm which has micro-images in a grid pattern is called microfiche. Microfiche are 4” X 6” (11cmX16cm) plastic cards on which photographic images are kept. Microfilm holds 230 documents(images) per card, one cubic foot box holds 6000 fiche cards or minimum of 13,80,000 pages. Microfilm and microfiche is used in COM(computer output microfiche) system. COM process of copying / printing data from electronic media onto microfilm. Super disk: Some of the features used in hard disk are being used in high capacity floppy disk called Super disk. Sony and Fuji films have developed 3.5 inch of 200MB floppy.
ZIP disk:
The Zip drive is a medium-capacity removable disk storage system that was introduced by Iomega in late 1994. Originally, Zip disks launched with capacities of 100 MB, but later versions increased this to first 250 MB and then 750 MB. The format became the most popular of the super-floppy type products which filled a place in the late 1990s portable storage market. However it was never popular enough to replace the 3.5-inch floppy disk nor could ever match the storage size available on rewritable CDs and later rewritable DVDs Magnetic Tape:
Magnetic tape is a medium for magnetic recording, made of a thin magnetizable coating on a long, narrow strip of plastic. It was developed in Germany, based on magnetic wire recording. A device that stores computer data on magnetic tape is a tape drive (tape unit, streamer). Today, other technologies can perform the functions of magnetic tape. In many cases these technologies are replacing tape. Despite this, innovation in the technology continues and tape is still widely used. Disadvantages of magnetic tape are no direct access, contents of a tape cannot be interpreted and verified directly, environmental problems (Temperature, dust etc. affects magnetic tape).
Accessing of data: Seek time: the time required to position the head over the proper track is called the seek time. Latency time: the time required to spin the needed data under the head is called the latency time. Total Access Time: for a disk for most of disk system is usually between 10 and 100 milliseconds. Output Devices:
An output device is any piece of computer hardware equipment used to communicate the results of data processing carried out by an information processing system (such as a computer) to the outside world.
In computing, input/output, or I/O, refers to the communication between an information processing system (such as a computer), and the outside world. Inputs are the signals or data sent to the system, and outputs are the signals or data sent by the system to the outside. Output device translate the processed in computer from Machine coded form into human understandable form. Output device of computer are types of peripheral hardware connected, that is connected to the computer, either using cables or over a wireless network. doesn't matter whether you have desktop computers, laptop computers, supercomputers, etc., you will require at least one computer output device. Examples of output devices: Speakers, Headphones, Screen (Monitor), Printer Output can exist in two forms:
i) Soft Copy Output
ii) Hard Copy Output
A Soft Copy is the unprinted digital document file. It can usually be viewed through an appropriate editing program, such as word processing programs, database programs, or presentation software, depending on the file type.
It can be transported from one computer to another through file transfer/downloading mechanisms such as ftp or http, as an email attachment, or through USB drives and other disk drives. Keeping a digital copy of a document can allow easy editing of it later on.
Using soft copies of work over traditional printed documents eliminates the need for paper and ink. Multiple copies of the same document can be kept in different versions, allowing the user to easily backtrack to an earlier version. Also, soft copies are more easily manipulated by users than hard copies, which can be both an advantage and a disadvantage. When soft copies are kept on storage devices, they conserve office space. Softcopy documents are more portable compared to hardcopy because it is not bulky like hardcopy. Soft copy refers to output display in the screen. Monitor is most commonly used soft copy output device. Monitor:
A monitor or display (also called screen or visual display unit) is an electronic visual display for computers. A computer monitor is an electronic device that shows pictures. A monitor is usually used to see programs on a computer. A monitor may be used to watch television if it is connected to a device that has a television tuner. Some models of monitor can be used as a television, and some televisions are used with computers. A monitor has a better display resolution than a television to make it easier to see smaller letters and graphics on. There are two main types of monitors:
The CRT monitor, which is big and heavy. It is the oldest technology used by monitors. It looks like a television, but has a bigger display resolution and often a higher frequency. CRT stands for cathode-ray tube.
The LCD or LED monitor, which is thin, flat, and lightweight. It is a newer technology than CRTs. The quality can be the same or even better than a CRT, but this type of monitor usually costs more than a CRT.
In the early 21st century the price of Video projectors has fallen and they are now used in many places to produce very large images. These use a range of different technologies to make the image including LCD - Liquid crystal display, LED - Light Emitting Diode which uses very small mirrors to direct the light
Projector: It is a hardware device, with which an image like a computer screen is projected onto a flat screen. Image data is sent to the video card, by the computer which is then translated into a video image and sent to the projector. A projector is often used in meetings or to make presentations, because they allow for a large image to be shown, with which the display is available for a large audience. Hard Copy Output Hard copy output refers to recording letters, picture on permanent medium such as paper or film. Printer, plotter are most commonly used hard copy output device. Printers & Plotters are main hard copy output devices. Printer is an external hardware device, which takes processed data from the computer to generate a hard copy of the data. After the monitors, printers are the most used peripherals on computers and they are commonly used to print text data, images, etc. Printers can be classified into different types in several ways. First, the printers can be divided into three categories by the way they print.
Serial Printers: Also called a character printer. Print a single character at a time. They are usually inexpensive and slow.
Line Printers: Print a line at a time. They are expensive and very fast. Line printers use a band, a chain, etc.
Page Printers: Also called a laser printer. Print a page at a time. They usually use a laser to produce page images. Quality is best. This is a little bit expensive, but the price of the personal laser printer is decreasing.
Second, printers can be classified into two forms according to the use of a hammer.
Impact Printers: Hammer hits ribbons, papers or print head. Dot-matrix, Daisy-wheel printers and Line printers are the example. Noisy.
Nonimpact Printers: They do not have the hammer and do not hit. An example is an ink-jet and laser printer.
Another classification can be made by the way they form characters.
Bit-Mapped Printers: Images are formed from groups of dots and can be placed anywhere on the page. They have many printing options and good printing quality.
Character-based Printers: Printer print characters into the lines and columns of a page. These printers use predefined set of characters and are restricted in position of characters.
Microcomputers use five kinds of printers. They are daisy wheel printers, chain printers, dot-matrix printers, ink-jet printers, and laser printers. Daisy-Wheel Printer : Daisy-Wheel is a printer mechanism that uses any kind of hub (wheel) having a set of spokes at the margin of the hub. The wheel can be removed to use a different character set. The end of each spoke is a raised image of a type character. When the wheel is turned and the required character is aligned to the print hammer, the character is then struck into a ribbon and onto a paper with the hammer. Daisy-Wheel Printer prints typewriter-like very high quality characters. However, they are slower and less reliable than dot-matrix printers. Microcomputer users seldom use this printer, because the better dot-matrix printers and inexpensive laser printers are available today. Chain Printer : A chain printer uses a printing mechanism that uses character typefaces linked together in a chain. The chain spins horizontally around a set of hammers aligned with each position. When the required character is in front of the selected print position, hammer in that position hits the paper into the ribbon against the character in the chain. This printer is not commonly found around microcomputers, because it is a very expensive, high-speed machine designed originally for mainframes and minicomputers. Chain printers are very reliable and can speed up to 3000 lines per minute. Dot-Matrix Printer : Dot-matrix printers are printers that write characters and form graphic images using one or two columns of tiny dots on a print head. The dot hammer moving serially across the paper strikes an inked-ribbon and creates images on paper. Dot matrix printers are popular printers used with microcomputers, because the printers are highly reliable and inexpensive. They are used for tasks where a high-quality image is not essential. Many users, however, move from dot printers to laser printers, because the price of laser printers is falling down. Several kinds of dot matrix printers are available with print heads that have 7, 9, 18, or 24 pins. Ink-Jet Printer : Ink-jet is a printer mechanism that sprays one or more color of ink at high speed onto the paper and produces high-quality printing. This printer also produces color printing as well as high-quality image. That is, ink-jet printers can be used for variety of color printing at a relatively low cost. Ink-jet printing has two methods: Continuous stream method and drop-on-demand method.
Laser Printer :
A laser printer is a printer that uses the electro photographic method used in a copy machine. The printer uses a laser beam light source to create images on a photographic drum. Then the images on the drum are treated with a magnetically charged toner and then are transferred onto a paper. A heat source is usually applied to make the images adhere. In 1984, Hewlett-Packard introduced the first desktop laser printer, called the LaserJet. The laser printer revolutionized personal computer printing and has spawned desktop publishing. The laser printer produces high-resolution letters and graphics quality images, so it is adopted in applications requiring high-quality output. Although a high-priced color laser
printer is also available in the market, a less expensive, desktop gray scale laser printer is widely used. Recently, the laser printer is gaining its market share dramatically, mainly because the lowered price and the quality Printers are also classified by the following characteristics:
Quality of type: The output produced by printers is said to be either letter quality (as good as a typewriter), near letter quality, or draft quality. Only daisy-wheel, ink-jet, and laser printers produce letter-quality type. Some dot-matrix printers claim letter-quality print, but if you look closely, you can see the difference.
Speed: Measured in characters per second (cps) or pages per minute (ppm), the speed of printers varies widely. Daisy-wheel printers tend to be the slowest, printing about 30 cps. Line printers are fastest (up to 3,000 lines per minute). Dot-matrix printers can print up to 500 cps, and laser printers range from about 4 to 20 text pages per minute.
Graphics: Some printers (daisy-wheel and line printers) can print only text. Other printers can print both text and graphics.
Fonts : Some printers, notably dot-matrix printers, are limited to one or a few fonts. In contrast, laser and ink-jet printers are capable of printing an almost unlimited variety of fonts. Daisy-wheel printers can also print different fonts, but you need to change the daisy wheel, making it difficult to mix fonts in the same document.
Thermal Printers: Thermal printers are not to be confused with thermal inkjet printers. Most thermal printers must use a special heat-sensitive paper, called thermal paper. The thermal paper has a coating that turns black when an electrically heated pin is pressed against it. Thermal printers are durable, but thermal paper is sensitive to light, water, and heat, and the text and images produced by thermal printers can fade over time. They are faster and quieter than dot matrix printers. Although used in cash registers and ATMs, they aren't really useful for everyday printing Plotters A plotter is a special-purpose output device that draws images with ink pens. That is, the plotter is a graphics printer for making sophisticated graphs, charts, maps, and three-dimensional graphics as well as high-quality colored documents. It can also produce larger size of documents. Plotters require data in a vector graphics format that can produce images with a series of lines. Plotter is uses one or more pens that can be raised, lowered and moved over the printing media to draw graphics or text. Modern plotter usually uses only 4 pens (cyan, magenta, yellow and black). Electronic plotters do not use pens. It is widely used in scientific and engineering field like CAD (Computer Aided Design). There are two main types of plotters:
Drum Plotter: This is a plotter that has a drum. A paper wraps the drum that rotates to produce plots. Pens in a drum plotter move across the paper while the drum is turning. A drum plotter is usually used to produce smaller drawings.
Flatbed Plotter: This is a plotter that has a bed. This is also called a table plotter. The plotter draws graphics on the paper placed on the bed. There are several size of beds. This plotter is usually used for producing large drawings
Unit of Measurement of Storage and Memory Devices : BIT : is abbreviation of the words Binary Digit and is the smallest unit of information. It is either '0' or '1' . The raw data fed into computer is first converted into an electrical pulses or BITS, as computer only works on '0' & '1'. The '0' and '1' of the binary system corresponds to ON and OFF of the flow of electricity in the computer's circuits. Computers work by recognizing the presence or absence of an electrical pulses or BITS at particular time. Byte : is the measuring computer's memory and size of program. One Byte is the string of eight binary digits (BITS). It may represent a single letter, number or other characters. Computer memory is expressed in terms of KB, MB, GB, TB
Word: is the basic unit for accessing computer storage on a particular machine, usually the size of each instruction and the size of the data value which is most efficiently processed. The word on a PA-RISC machine is 32-bits (4 bytes), while a word on the Classic HP 3000 is 16-bits (2 bytes). A byte is 8 bits and 16-bits is called a halfword on PA-RISC machines. There are Machine Instructions to load and store words, halfwords, and bytes. Computer having smaller word length is slower than other having larger word length. Word length is generally fixed for a computer. Now-a-days computers have word length of 16, 32, 64,128 and even more bits.
CPU Speed : is measure in megahertz. A 1MHz CPU can accomplish one million CPU cycles (tasks) in one second. MIPS- short form of Millions of Instructions Per Second. The task execution speed of computer is also measured in terms of MIPS. Now a days computers come with CPU speed of GHz (gigahertz) For example CPU speed of 0.5 GHz =512 MHz= 512 MIPS i.e. 512,000,000 instructions per second.
nibble 4 bit (b)
byte (B) 8 bit (b)
kilobyte (KB) 1024 B
megabyte (MB) 1024 KB
gigabyte (GB) 1024 MB
terabyte (TB) 1024 GB
petabyte (PB) 1024 TB
exabyte (EB) 1024 PB
zettabyte (ZB) 1024 EB
yottabyte (YB) 1024 ZB
Computer is fast and accurate electronic device capable of accepting data, store it, process it as predefined stored instructions and give the result.
Technically, a computer is a programmable machine. This means it can execute a programmed list of instructions and respond to new instructions that it is given. Today, however, the term is most often used to refer to the desktop and laptop computers that most people use. When referring to a desktop model, the term "computer" refer to everything together the monitor, keyboard, and mouse as the computer. If you want to be really technical, the box that holds the computer is called the "system unit."
Some of the major parts of a personal computer (or PC) include the motherboard, CPU, memory (or RAM), hard drive, and video card. While personal computers are by far the most common type of computers today, there are several other types of computers. For example, a "minicomputer" is a powerful computer that can support many users at once. A "mainframe" is a large, high-powered computer that can perform billions of calculations from multiple sources at one time. Finally, a "supercomputer" is a machine that can process billions of instructions a second and is used to calculate extremely complex calculations.
Diagram showing elements of Computer system and Logical connection Input Unit : Inserts data and instruction to main memory . Main Memory : Holds input data, instruction and processed result . Auxiliary Memory : Supports main memory and backing storage . Control Unit : Interrupt stored instruction in sequence . Issuing commands to all element of computer. ALU : Perform Arithmetic and Logical operations . Output Unit : Show/produce result of the processed information . Input Devices:
Any machine that feeds data into a computer. For example, a keyboard is an input device. Input devices establish the communication link between the user and computer system. There are various types of input devices. Input devices other than the keyboard are sometimes called alternate input devices. Mice, trackballs and light pens are all alternate input devices. Input Unit Keyboard Mouse Scanner Joystick Processing/System Unit
Keyboard Mouse Joystick Track Ball Light pen Touch screen Optical mark reader Optical character reader Magnetic ink character recognition Bar code reader Punch card & card reader Paper tape & paper tape reader Scanner
Keyboard:
The set of typewriter-like keys that enables you to enter data into a computer. Computer keyboards are similar to electric-typewriter keyboards but contain additional keys. The keys on computer keyboards are often classified as follows:
Alphanumeric keys -- letters and numbers
Punctuation keys -- comma, period, semicolon, and so on.
Special keys -- function keys, control keys, arrow keys, Caps Lock key, and so on.
The standard layout of letters, numbers, and punctuation is known as a QWERTY keyboard because the first six keys on the top row of letters spell QWERTY. The QWERTY keyboard was designed in the 1800s for mechanical typewriters and was actually designed to slow typists down to avoid jamming the keys. Another keyboard design, which has letters positioned for speed typing, is the Dvorak keyboard. The Dvorak keyboard was designed with the most common consonants on one side of the middle or home row and the vowels on the other side so that typing tends to alternate key strokes back and forth between hands. Although the Dvorak keyboard has never been widely used, it has adherents.
There is no standard computer keyboard, although many manufacturers imitate the keyboards of PCs. There are actually three different PC keyboards: the original PC keyboard, with 84 keys; the AT keyboard, also with 84 keys; and the enhanced keyboard, with 101 or more keys. The three differ somewhat in the placement of function keys, the Control key, the Return key, and the Shift keys.
In addition to these keys, IBM keyboards contain the following keys: Page Up, Page Down, Home, End, Insert, Pause, Num Lock, Scroll Lock, Break, Caps Lock, Print Screen.
There are several different types of keyboards for the Apple Macintosh. All of them are called ADB keyboards because they connect to the Apple Desktop bus (ADB). The two main varieties of Macintosh keyboards are the standard keyboard and the extended keyboard, which has 15 additional special-function keys.
A circuit called Keyboard_encoder detects key press on keyboard. It generates binary code & is send to the system unit. Keyboards may be wired or wireless but they always communicate with the computer via PS/2 or USB connections, usually located on the motherboard. Even though the keyboard sits outside the main computer housing, it is an essential part of the complete system. Mouse:
In computing, a mouse is a pointing device that functions by detecting two-dimensional motion relative to its supporting surface. Physically, a mouse consists of an object held under one of the user's hands, with one or more buttons. It sometimes features other elements, such as "wheels", which allow the user to perform various system-dependent operations, or extra buttons or features that can add more control or dimensional input. The mouse's motion typically translates into the motion of a pointer on a display, which allows for fine control of a graphical user interface.
Independently, Douglas Engelbart at the Stanford Research Institute invented the first mouse prototype in 1963,[4] with the assistance of his colleague Bill English. They named the device the mouse as early models had a cord attached to the rear part of the device looking like a tail and generally resembling the common mouse and pioneered by Xerox in the 1970s, the mouse is one of the great breakthroughs in computer world because it frees the user to a large extent from using the keyboard. In particular, the mouse is important for graphical user interfaces because you can simply point to options and objects and click a mouse button. Such applications are often called point-and-click programs. The mouse is also useful for graphics programs that allow you to draw pictures by using the mouse like a pen, pencil, or paintbrush. There are three basic types of mice:
1. Mechanical: Has a rubber or metal ball on its underside that can roll in all directions. Mechanical sensors within the mouse detect the direction the ball is rolling and move the screen pointer accordingly.
2. Optomechanical: Same as a mechanical mouse, but uses optical sensors to detect motion of the ball.
3. Optical: Optical mice make use of one or more light-emitting diodes (LEDs) and an imaging array of photodiodes to detect movement relative to the underlying surface, rather than internal moving parts as does a mechanical mouse. A laser mouse is an optical mouse that uses coherent (laser) light.
Mice connect to PCs in one of several ways:
1. Serial mice connect directly to an RS-232C serial port or a PS/2 port. This is the simplest type of connection.
2. USB mice.
Cordless mice aren't physically connected at all. Instead they rely on infrared or radio waves to communicate with the computer. Cordless mice are more expensive than both serial and USB mice, but they do eliminate the cord, which can sometimes get in the way. Scanner :
In computing, an image scanner—often abbreviated to just scanner—is a device that optically scans images, printed text, handwriting, or an object, and converts it to a digital image. Common examples found in offices are variations of the desktop (or flatbed) scanner where the document is placed on a glass window for scanning. A scanner works
by digitizing an image -- dividing it into a grid of boxes and representing each box with either a zero or a one, depending on whether the box is filled in. (For color and gray scaling, the same principle applies, but each box is then represented by up to 24 bits.) The resulting matrix of bits, called a bit map, can then be stored in a file, displayed on a screen, and manipulated by programs.
Optical scanners do not distinguish text from illustrations; they represent all images as bit maps. Therefore, you cannot directly edit text that has been scanned. To edit text read by an optical scanner, you need an optical character recognition (OCR ) system to translate the image into ASCII characters. Most optical scanners sold today come with OCR packages.. Trackball:
A trackball is a pointing device consisting of a ball held by a socket containing sensors to detect a rotation of the ball about two axes—like an upside-down mouse with an exposed protruding ball. The user rolls the ball with the thumb, fingers, or the palm of the hand to move a pointer. Compared with a mouse, a trackball has no limits on effective travel; at times, a mouse can reach an edge of its working area while the operator still wishes to move the screen pointer farther. With a trackball, the operator just continues rolling.
Large trackballs are common on CAD workstations for easy precision. Before the advent of the touchpad, small trackballs were common on portable computers, where there may be no desk space on which to run a mouse. Some small thumb balls clip onto the side of the keyboard and have integral buttons with the same function as mouse buttons. The trackball was invented by Tom Cranston and Fred Longstaff as part of the Royal Canadian Navy's DATAR system in 1952, eleven years before the mouse was invented. This first trackball used a Canadian five-pin bowling ball. Joystick:
A joystick is an input device consisting of a stick that pivots on a base and reports its angle or direction to the device it is controlling. Potentiometers within the base translate X-Y position information into voltage which can then be encoded in binary for input to digital system. They often have supplementary switches on them to control.
Joysticks are often used to control video games, and usually have one or more push-buttons whose state can also be read by the computer. A popular variation of the joystick used on modern video game consoles is the analog stick. Joysticks are also used for controlling machines such as cranes, trucks, underwater unmanned vehicles, wheelchairs, surveillance cameras etc.. Small finger-operated joysticks have been adopted as input devices for smaller electronic equipment such as mobile phones. Light pen:
A light pen is a computer input device in the form of a light-sensitive stick used in conjunction with a computer's CRT TV set or monitor. It allows the user to point to displayed objects, or draw on the screen, in a similar way to a touch screen but with greater positional accuracy. It was long thought that a light pen can work with any CRT-based display, but not with LCD screens, projectors and other display devices. A light pen works by sensing the sudden small change in brightness of a point on the screen when the electron gun refreshes that spot. By noting exactly where the scanning has reached at that moment, the X,Y position of the pen can be resolved. This is usually achieved by the light pen causing an interrupt, at which point the scan position can be read from a special register, or computed from a counter or timer. The pen position is updated on every refresh of the screen
The first light pen was created around 1952 as part of the Whirlwind project at Massachusetts Institute of Technology.
A Touchpad (or Trackpad) is a pointing device featuring a tactile sensor, a specialized surface that can translate the motion and position of a user's fingers to a relative position on screen. Touchpad is a common feature of laptop computers, and are also used as a substitute for a mouse where desk space is scarce. Because they vary in size, they can also be found on personal digital assistants (PDAs) and some portable media players. Wireless touchpads are also available as detached accessories. Optical character recognition:- usually abbreviated to OCR, is the mechanical or electronic translation of scanned images of handwritten, typewritten or printed text into machine-encoded text. It is widely used to convert books and documents into electronic files, to computerize a record-keeping system in an office, or to publish the text on a website. OCR makes it possible to edit the text, search for a word or phrase, store it more compactly, display or print a copy free of scanning artifacts, and apply techniques such as machine translation, text-to-speech and text mining to it. OCR is a field of research in pattern recognition, artificial intelligence and computer vision. Magnetic Ink Character Recognition, or MICR, is a character recognition technology used primarily by the banking industry to facilitate the processing of cheques and makes up the routing number and account number at the bottom of a check. The technology allows computers to read information (such as account numbers) off printed documents. Unlike barcodes or similar technologies, however, MICR codes can be easily read by humans.
MICR characters are printed in special typefaces with a magnetic ink or toner, usually containing iron oxide. As a machine decodes the MICR text, it first magnetizes the characters in the plane of the paper. Then the characters are
passed over a MICR read head, a device similar to the playback head of a tape recorder. As each character passes over the head it produces a unique waveform that can be easily identified by the system.
The use of magnetic printing allows the characters to be read reliably even if they have been overprinted or obscured by other marks, such as cancellation stamps and signature. The error rate for the magnetic scanning of a typical check is smaller than with optical character recognition systems.
A Barcode Reader (or Barcode Scanner) is an electronic device for reading printed barcodes. Like a flatbed scanner, it consists of a light source, a lens and a light sensor translating optical impulses into electrical ones. Additionally, nearly all barcode readers contain decoder circuitry analyzing the barcode's image data provided by the sensor and sending the barcode's content to the scanner's output port. Central Processing Unit (CPU)
The central processing unit (CPU) is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The form, design and implementation of CPUs have changed dramatically since the earliest examples, but their fundamental operation remains much the same.
On large machines, CPUs require one or more printed circuit boards. On personal computers and small workstations, the CPU is housed in a single silicon chip called a microprocessor. Since the 1970s the microprocessor class of CPUs has almost completely overtaken all other CPU implementations. Modern CPUs are large scale integrated circuits in packages typically less than four centimeters square, with hundreds of connecting pins.
Two typical components of a CPU are the arithmetic logic unit (ALU), which performs arithmetic and logical operations, and the control unit(CU), which extracts instructions from memory and decodes and executes them, calling on the ALU when necessary. Control Unit : The control unit of the CPU contains circuitry that uses electrical signals to direct the entire computer system to carry out stored program instructions. The control unit does not execute program instructions; rather, it directs other parts of the system to do so. The control unit must communicate with both the arithmetic/logic unit and memory The control unit is one of the most important parts of a microprocessor for the reason that it is in charge of the entire process, that is the machine cycle. The CPU deals with each instruction it is given in a series of steps. Each step is repeated for each instruction. This series of steps is called the machine cycle. It involves:
fetching an instruction from memory;
decoding the instruction;
transferring the data;
executing the instruction.
The control unit makes sure that all of those actions are carried out. It also manages all the other components on the CPU. Arithmetic and Logic Unit :
In computing, an arithmetic logic unit (ALU) is a digital circuit that performs arithmetic and logical operations. The ALU is a fundamental building block of the central processing unit of a computer, and even the simplest microprocessors contain one for purposes such as maintaining timers. It contains circuit to perform the arithmetical operation on numbers and logical tests for equality, greater then and less then between operations. Final results are transferred to memory. Data Storage Device
A data storage device is a device for recording (storing) information (data). Recording can be done using virtually any form of energy, spanning from manual muscle power in handwriting, to acoustic vibrations in phonographic recording, to electromagnetic energy modulating magnetic tape and optical discs.
A storage device may hold information, process information, or both. A device that only holds information is a recording medium. Devices that process information (data storage equipment) may either access a separate portable (removable) recording medium or a permanent component to store and retrieve information.
Electronic data storage is storage which requires electrical power to store and retrieve that data. Electromagnetic data may be stored in either an analog or digital format on a variety of media. This type of data is considered to be electronically encoded data, whether or not it is electronically stored in a semiconductor device, for it is certain that a semiconductor device was used to record it on its medium. Most electronically processed data storage media (including some forms of computer data storage) are considered permanent (non-volatile) storage, that is, the data will remain stored when power is removed from the device. In contrast, most electronically stored information within most types of semiconductor (computer chips) microcircuits are volatile memory, for it vanishes if power is removed.
Primary or Main Memory: Primary storage (or main memory or internal memory), often referred to simply as memory, is the only one directly accessible to the CPU. The CPU continuously reads instructions stored there and executes them as required. Any data actively operated on is also stored there in uniform manner. Main memory is divided into two parts : RAM (Random Access Memory) and ROM (Read Only Memory) RAM (Random Access Memory) Random Access Memory is responsible for storing the instruction and data that the computer is using at that present moment in time. It is volatile memory, which means item stored in RAM are lost when the power to the computer is turned off. There are mainly two types of RAM : SRAM (Static Random Access Memory)
Faster and more reliable than any form of DRAM. The static refers to the fact that it does not have to be re-energized as often as DRAM. The access time is 10-100ns and does not need refresh cycles. a bit of data is stored using the state of a flip-flop. This form of RAM is more expensive to produce, but is generally faster and requires less power. DRAM (Dynamic Random Access Memory ) DRAM stores a bit of data using a transistor and capacitor pair, which together comprise a memory cell. The capacitor holds a high or low charge (1 or 0, respectively), and the transistor acts as a switch that lets the control circuitry on the chip read the capacitor's state of charge or change it. Due to leakage the capacitor discharges gradually and memory cell loses the information. Therefore to preserve the information the memory has to be refreshed periodically. It is popular as high density and low price. Access time is 40-70 ns or less. As this form of memory is less expensive to produce than static RAM, it is the predominant form of computer memory used in modern computers. The other types of DRAM is Synchronous DRAM(SDRAM) and Rambus DRAM(RDRDM) which is much faster than DRAM. ROM (Read Only Memory)
Read-only memory (ROM) is a class of storage medium used in computers and other electronic devices. Data stored in ROM cannot be modified, or can be modified only slowly or with difficulty, so it is mainly used to distribute firmware (software that is very closely tied to specific hardware, and unlikely to need frequent updates). ROM is a permanent type memory. Its contents are not lost when power supply goes off. Its contents are decided by manufacturer and written at the time of manufacture. Generally the ROM of microcomputer contains system programs for handling the operating system. The user programmable ROMs are also available in the following types. Programmable Read-Only Memory (PROM), or One-Time Programmable ROM (OTP), can be written to or programmed via a special device called a PROM programmer. Typically, this device uses high voltages to permanently destroy or create internal links (fuses or antifuses) within the chip. Consequently, a PROM can only be programmed once. Erasable Programmable Read-Only Memory (EPROM) can be erased by exposure to strong ultraviolet light (typically for 10 minutes or longer), then rewritten with a process that again needs higher than usual voltage applied. Repeated exposure to UV light will eventually wear out an EPROM, but the staying power of most EPROM chips exceeds 1000 cycles of erasing and reprogramming. EPROM chip packages can often be identified by the prominent quartz "window" which allows UV light to enter. After programming, the window is typically covered with a label to prevent accidental erasure. Some EPROM chips are factory-erased before they are packaged, and include no window; these are effectively PROM. Electrically Erasable Programmable Read-Only Memory (EEPROM) is based on a similar semiconductor structure to EPROM, but allows its entire contents (or selected banks) to be electrically erased, then rewritten electrically, so that they need not be removed from the computer (or camera, MP3 player, etc.). Writing or flashing an EEPROM is much slower (milliseconds per bit) than reading from a ROM or writing to a RAM (nanoseconds in both cases). Electrically Alterable Read-Only Memory (EAROM) is a type of EEPROM that can be modified one bit at a time. Writing is a very slow process and again needs higher voltage (usually around 12 V) than is used for read access. EAROMs are intended for applications that require infrequent and only partial rewriting. EAROM may be used as non-volatile storage for critical system setup information; in many applications, EAROM has been supplanted by CMOS RAM supplied by mains power and backed-up with a lithium battery. Flash memory (or simply flash) is a modern type of EEPROM invented in 1984. Flash memory can be erased and rewritten faster than ordinary EEPROM, and newer designs feature very high endurance (exceeding 1,000,000 cycles). Modern NAND flash makes efficient use of silicon chip area, resulting in individual ICs with a capacity as high as 32 GB as of 2007; this feature, along with its endurance and physical durability, has allowed NAND flash to replace magnetic in some applications (such as USB flash drives). Flash
memory is sometimes called flash ROM or flash EEPROM when used as a replacement for older ROM types, but not in applications that take advantage of its ability to be modified quickly and frequently. By applying write protection, some types of reprogrammable ROMs may temporarily become read-only memory CACHE MEMORY: This is a small amount of high speed memory that lies between the CPU and main memory. The memory contains frequently required data and instructions. When CPU needs to access any information or data it first checks if the data is available in the cache memory. Only if needed data is unavailable with cache memory it will make a trip to the main memory. Usually systems come with 256 KB to 4MB of cache memory.
A CPU cache is a cache used by the central processing unit of a computer to reduce the average time to access memory. The cache is a smaller, faster memory which stores copies of the data from the most frequently used main memory locations. As long as most memory accesses are cached memory locations, the average latency (delays in transmitting data between the CPU and RAM) of memory accesses will be closer to the cache latency than to the latency of main memory Most modern computers have 2 types or Layers of Cache Level 1 (L1)and Level 2 (L2). L1 Cache is built directly into the processor chip, faster and small capacity than L2 Cache. L2 Cache (high speed SRAM) is larger in capacity, slower than L1 Cache and lies between CPU and Main Memory. Multi-level caches generally operate by checking the smallest Level 1 (L1) cache first; if it hits, the processor proceeds at high speed. If the smaller cache misses, the next larger cache (L2) is checked, and so on, before external memory is checked. Secondary or Auxiliary Memory: Secondary storage (also known as external memory or auxiliary storage), differs from primary storage in that it is not directly accessible by the CPU. The computer usually uses its input/output channels to access secondary storage and transfers the desired data using intermediate area in primary storage. Secondary storage does not lose the data when the device is powered down—it is non-volatile. Per unit, it is typically also two orders of magnitude less expensive than primary storage. Consequently, modern computer systems typically have two orders of magnitude more secondary storage than primary storage and data are kept for a longer time there.
In modern computers, hard disk drives are usually used as secondary storage. The time taken to access a given byte of information stored on a hard disk is typically a few thousandths of a second, or milliseconds. By contrast, the time taken to access a given byte of information stored in random access memory is measured in billionths of a second, or nanoseconds. This illustrates the significant access-time difference which distinguishes solid-state memory from rotating magnetic storage devices: hard disks are typically about a million times slower than memory. Rotating optical storage devices, such as CD and DVD drives, have even longer access times. With disk drives, once the disk read/write head reaches the proper placement and the data of interest rotates under it, subsequent data on the track are very fast to access. As a result, in order to hide the initial seek time and rotational latency, data are transferred to and from disks in large contiguous blocks.
Some other examples of secondary storage technologies are: flash memory (e.g. USB flash drives ), floppy disks, magnetic tape, paper tape, punched cards, standalone RAM disks, and Iomega Zip drives. Hard disks :
A hard disk drive (HDD; also hard drive, hard disk, or disk drive) is a device for storing and retrieving digital information, primarily computer data. It consists of one or more rigid (hence "hard") rapidly rotating discs (often referred to as platters), coated with magnetic material and with magnetic heads arranged to write data to the surfaces and read it from them. Hard drives are classified as non-volatile, random access, digital, magnetic, data storage devices. Introduced by IBM in 1956, hard disk drives have decreased in cost and physical size over the years while dramatically increasing in capacity and speed. Hard disk drives have been the dominant device for secondary storage of data in general purpose computers since the early 1960s. They have maintained this position because advances in their recording capacity, cost, reliability, and speed have kept pace with the requirements for secondary storage As disk pack is sealed containers are dust free and they allow very high speed usually 4200rpm-15000rpm. A hard disk may have more than 10,000 tracks per surface bit density 15,00 bits per inch. Data transfer rate 33.3 to 160MB per second. The hard disk come in 2.5 inch, 3.5 inch and 5.25 inch diameter. Hard disk controller are used to interface hard disk to a processor. Floppy disk:
A floppy disk is a disk storage medium composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles. They are read and written by a floppy disk drive (FDD). Floppy disks, initially as 8-inch (200 mm) media and later in 5.25-inch (133 mm) and 3.5-inch (89 mm) sizes, were a ubiquitous form of data storage and exchange from the mid-1970s well into the first decade of the 21st century.
By 2010, computer motherboards were rarely manufactured with floppy drive support; 3 1⁄2" floppies could be used with an external USB drive, but 5 1⁄4", 8", and non-standard drives could only be handled by old equipment.
While floppy disk drives still have some limited uses, they have been superseded by data storage methods with much greater capacity, such as USB flash drives, portable external hard disk drives, optical discs, memory cards, and computer networks. Optical Storage Disk: It was developed from video disk technology during early 1980s
In computing and optical disc recording technologies, an optical disc is a flat, usually circular disc which encodes binary data (bits) in the form of pits (binary value of 0 or off, due to lack of reflection when read) and lands (binary value of 1 or on, due to a reflection when read) on a special material (often aluminium on one of its flat surfaces. The encoding material sits atop a thicker substrate (usually polycarbonate) which makes up the bulk of the disc and forms a dust defocusing layer. The encoding pattern follows a continuous, spiral path covering the entire disc surface and extending from the innermost track to the outermost track. The data is stored on the disc with a laser or stamping machine, and can be accessed when the data path is illuminated with a laser diode in an optical disc drive which spins the disc at speeds of about 200 to 4000RPM or more, depending on the drive type, disc format, and the distance of the read head from the center of the disc (inner tracks are read at a faster disc speed). The pits or bumps distort the reflected laser light, hence most optical discs (except the black discs of the original PlayStation video game console) characteristically have an shining appearance created by the grooves of the reflective layer. The reverse side of an optical disc usually has a printed label, generally made of paper but sometimes printed or stamped onto the disc itself. This side of the disc contains the actual data and is typically coated with a transparent material, usually polish. Unlike the 3½-inch floppy disk, most optical discs do not have an integrated protective casing and are therefore susceptible to data transfer problems due to scratches, fingerprints, and other environmental problems.
Optical discs are usually between 7.6 and 30 cm (3 to 12 in) in diameter, with 12 cm (4.75 in) being the most common size. A typical disc is about 1.2 mm (0.05 in) thick, while the track pitch (distance from the center of one track to the center of the next) is typically 1.6 μm.
An optical disc is designed to support one of three recording types: read-only (e.g.: CD and CD-ROM), recordable (write-once, e.g. CD-R), or re-recordable (rewritable, e.g. CD-RW). Write-once optical discs commonly have an organic dye recording layer between the substrate and the reflective layer. Rewritable discs typically contain an alloy recording layer composed of a phase change material, most often AgInSbTe, an alloy of silver, indium, antimony and tellurium.
Optical discs are most commonly used for storing music (e.g. for use in a CD player), video (e.g. for use in a DVD (Digital Versatile Disk) player), or data and programs for personal computers (PC). The Optical Storage Technology Association (OSTA) promotes standardized optical storage formats. Although optical discs are more durable than earlier audio-visual and data storage formats, they are susceptible to environmental and daily-use damage. Libraries and archives enact optical media preservation procedures to ensure continued usability in the computer's optical disc drive or corresponding disc player
A USB flash drive : is a data storage device that consists of flash memory with an integrated Universal Serial Bus (USB) interface. USB flash drives are typically removable and rewritable, and physically much smaller than a floppy disk. Most weigh less than 30 g. As of September 2011 drives of 256 gigabytes (GB) are available, and storage capacities as large as 2 terabytes (TB) are planned, with steady improvements in size and price per capacity expected. Some allow up to 100,000 write/erase cycles (depending on the exact type of memory chip used) and 10 years shelf storage time.
USB flash drives are often used for the same purposes for which floppy disks or CD-ROMs were used. They are smaller, faster, have thousands of times more capacity, and are more durable and reliable because they have no moving parts. Until approximately 2005, most desktop and laptop computers were supplied with floppy disk drives, but floppy disk drives have been dumped in favor of USB ports.
A flash drive consists of a small printed circuit board carrying the circuit elements and a USB connector, insulated electrically and protected inside a plastic, metal, or rubberized case which can be carried in a pocket or on a key chain, for example. The USB connector may be protected by a removable cap or by retracting into the body of the drive, although it is not likely to be damaged if unprotected. Most flash drives use a standard type-A USB connection allowing plugging into a port on a personal computer, but drives for other interfaces also exist.
USB flash drives draw power from the computer via external USB connection. Some devices combine the functionality of a digital audio player with USB flash storage; they require a battery only when used to play music. MICROFILM: It is a high resolution film on which photographic records of documents or other materials are kept in reduced size. A sheet of microfilm which has micro-images in a grid pattern is called microfiche. Microfiche are 4” X 6” (11cmX16cm) plastic cards on which photographic images are kept. Microfilm holds 230 documents(images) per card, one cubic foot box holds 6000 fiche cards or minimum of 13,80,000 pages. Microfilm and microfiche is used in COM(computer output microfiche) system. COM process of copying / printing data from electronic media onto microfilm. Super disk: Some of the features used in hard disk are being used in high capacity floppy disk called Super disk. Sony and Fuji films have developed 3.5 inch of 200MB floppy.
ZIP disk:
The Zip drive is a medium-capacity removable disk storage system that was introduced by Iomega in late 1994. Originally, Zip disks launched with capacities of 100 MB, but later versions increased this to first 250 MB and then 750 MB. The format became the most popular of the super-floppy type products which filled a place in the late 1990s portable storage market. However it was never popular enough to replace the 3.5-inch floppy disk nor could ever match the storage size available on rewritable CDs and later rewritable DVDs Magnetic Tape:
Magnetic tape is a medium for magnetic recording, made of a thin magnetizable coating on a long, narrow strip of plastic. It was developed in Germany, based on magnetic wire recording. A device that stores computer data on magnetic tape is a tape drive (tape unit, streamer). Today, other technologies can perform the functions of magnetic tape. In many cases these technologies are replacing tape. Despite this, innovation in the technology continues and tape is still widely used. Disadvantages of magnetic tape are no direct access, contents of a tape cannot be interpreted and verified directly, environmental problems (Temperature, dust etc. affects magnetic tape).
Accessing of data: Seek time: the time required to position the head over the proper track is called the seek time. Latency time: the time required to spin the needed data under the head is called the latency time. Total Access Time: for a disk for most of disk system is usually between 10 and 100 milliseconds. Output Devices:
An output device is any piece of computer hardware equipment used to communicate the results of data processing carried out by an information processing system (such as a computer) to the outside world.
In computing, input/output, or I/O, refers to the communication between an information processing system (such as a computer), and the outside world. Inputs are the signals or data sent to the system, and outputs are the signals or data sent by the system to the outside. Output device translate the processed in computer from Machine coded form into human understandable form. Output device of computer are types of peripheral hardware connected, that is connected to the computer, either using cables or over a wireless network. doesn't matter whether you have desktop computers, laptop computers, supercomputers, etc., you will require at least one computer output device. Examples of output devices: Speakers, Headphones, Screen (Monitor), Printer Output can exist in two forms:
i) Soft Copy Output
ii) Hard Copy Output
A Soft Copy is the unprinted digital document file. It can usually be viewed through an appropriate editing program, such as word processing programs, database programs, or presentation software, depending on the file type.
It can be transported from one computer to another through file transfer/downloading mechanisms such as ftp or http, as an email attachment, or through USB drives and other disk drives. Keeping a digital copy of a document can allow easy editing of it later on.
Using soft copies of work over traditional printed documents eliminates the need for paper and ink. Multiple copies of the same document can be kept in different versions, allowing the user to easily backtrack to an earlier version. Also, soft copies are more easily manipulated by users than hard copies, which can be both an advantage and a disadvantage. When soft copies are kept on storage devices, they conserve office space. Softcopy documents are more portable compared to hardcopy because it is not bulky like hardcopy. Soft copy refers to output display in the screen. Monitor is most commonly used soft copy output device. Monitor:
A monitor or display (also called screen or visual display unit) is an electronic visual display for computers. A computer monitor is an electronic device that shows pictures. A monitor is usually used to see programs on a computer. A monitor may be used to watch television if it is connected to a device that has a television tuner. Some models of monitor can be used as a television, and some televisions are used with computers. A monitor has a better display resolution than a television to make it easier to see smaller letters and graphics on. There are two main types of monitors:
The CRT monitor, which is big and heavy. It is the oldest technology used by monitors. It looks like a television, but has a bigger display resolution and often a higher frequency. CRT stands for cathode-ray tube.
The LCD or LED monitor, which is thin, flat, and lightweight. It is a newer technology than CRTs. The quality can be the same or even better than a CRT, but this type of monitor usually costs more than a CRT.
In the early 21st century the price of Video projectors has fallen and they are now used in many places to produce very large images. These use a range of different technologies to make the image including LCD - Liquid crystal display, LED - Light Emitting Diode which uses very small mirrors to direct the light
Projector: It is a hardware device, with which an image like a computer screen is projected onto a flat screen. Image data is sent to the video card, by the computer which is then translated into a video image and sent to the projector. A projector is often used in meetings or to make presentations, because they allow for a large image to be shown, with which the display is available for a large audience. Hard Copy Output Hard copy output refers to recording letters, picture on permanent medium such as paper or film. Printer, plotter are most commonly used hard copy output device. Printers & Plotters are main hard copy output devices. Printer is an external hardware device, which takes processed data from the computer to generate a hard copy of the data. After the monitors, printers are the most used peripherals on computers and they are commonly used to print text data, images, etc. Printers can be classified into different types in several ways. First, the printers can be divided into three categories by the way they print.
Serial Printers: Also called a character printer. Print a single character at a time. They are usually inexpensive and slow.
Line Printers: Print a line at a time. They are expensive and very fast. Line printers use a band, a chain, etc.
Page Printers: Also called a laser printer. Print a page at a time. They usually use a laser to produce page images. Quality is best. This is a little bit expensive, but the price of the personal laser printer is decreasing.
Second, printers can be classified into two forms according to the use of a hammer.
Impact Printers: Hammer hits ribbons, papers or print head. Dot-matrix, Daisy-wheel printers and Line printers are the example. Noisy.
Nonimpact Printers: They do not have the hammer and do not hit. An example is an ink-jet and laser printer.
Another classification can be made by the way they form characters.
Bit-Mapped Printers: Images are formed from groups of dots and can be placed anywhere on the page. They have many printing options and good printing quality.
Character-based Printers: Printer print characters into the lines and columns of a page. These printers use predefined set of characters and are restricted in position of characters.
Microcomputers use five kinds of printers. They are daisy wheel printers, chain printers, dot-matrix printers, ink-jet printers, and laser printers. Daisy-Wheel Printer : Daisy-Wheel is a printer mechanism that uses any kind of hub (wheel) having a set of spokes at the margin of the hub. The wheel can be removed to use a different character set. The end of each spoke is a raised image of a type character. When the wheel is turned and the required character is aligned to the print hammer, the character is then struck into a ribbon and onto a paper with the hammer. Daisy-Wheel Printer prints typewriter-like very high quality characters. However, they are slower and less reliable than dot-matrix printers. Microcomputer users seldom use this printer, because the better dot-matrix printers and inexpensive laser printers are available today. Chain Printer : A chain printer uses a printing mechanism that uses character typefaces linked together in a chain. The chain spins horizontally around a set of hammers aligned with each position. When the required character is in front of the selected print position, hammer in that position hits the paper into the ribbon against the character in the chain. This printer is not commonly found around microcomputers, because it is a very expensive, high-speed machine designed originally for mainframes and minicomputers. Chain printers are very reliable and can speed up to 3000 lines per minute. Dot-Matrix Printer : Dot-matrix printers are printers that write characters and form graphic images using one or two columns of tiny dots on a print head. The dot hammer moving serially across the paper strikes an inked-ribbon and creates images on paper. Dot matrix printers are popular printers used with microcomputers, because the printers are highly reliable and inexpensive. They are used for tasks where a high-quality image is not essential. Many users, however, move from dot printers to laser printers, because the price of laser printers is falling down. Several kinds of dot matrix printers are available with print heads that have 7, 9, 18, or 24 pins. Ink-Jet Printer : Ink-jet is a printer mechanism that sprays one or more color of ink at high speed onto the paper and produces high-quality printing. This printer also produces color printing as well as high-quality image. That is, ink-jet printers can be used for variety of color printing at a relatively low cost. Ink-jet printing has two methods: Continuous stream method and drop-on-demand method.
Laser Printer :
A laser printer is a printer that uses the electro photographic method used in a copy machine. The printer uses a laser beam light source to create images on a photographic drum. Then the images on the drum are treated with a magnetically charged toner and then are transferred onto a paper. A heat source is usually applied to make the images adhere. In 1984, Hewlett-Packard introduced the first desktop laser printer, called the LaserJet. The laser printer revolutionized personal computer printing and has spawned desktop publishing. The laser printer produces high-resolution letters and graphics quality images, so it is adopted in applications requiring high-quality output. Although a high-priced color laser
printer is also available in the market, a less expensive, desktop gray scale laser printer is widely used. Recently, the laser printer is gaining its market share dramatically, mainly because the lowered price and the quality Printers are also classified by the following characteristics:
Quality of type: The output produced by printers is said to be either letter quality (as good as a typewriter), near letter quality, or draft quality. Only daisy-wheel, ink-jet, and laser printers produce letter-quality type. Some dot-matrix printers claim letter-quality print, but if you look closely, you can see the difference.
Speed: Measured in characters per second (cps) or pages per minute (ppm), the speed of printers varies widely. Daisy-wheel printers tend to be the slowest, printing about 30 cps. Line printers are fastest (up to 3,000 lines per minute). Dot-matrix printers can print up to 500 cps, and laser printers range from about 4 to 20 text pages per minute.
Graphics: Some printers (daisy-wheel and line printers) can print only text. Other printers can print both text and graphics.
Fonts : Some printers, notably dot-matrix printers, are limited to one or a few fonts. In contrast, laser and ink-jet printers are capable of printing an almost unlimited variety of fonts. Daisy-wheel printers can also print different fonts, but you need to change the daisy wheel, making it difficult to mix fonts in the same document.
Thermal Printers: Thermal printers are not to be confused with thermal inkjet printers. Most thermal printers must use a special heat-sensitive paper, called thermal paper. The thermal paper has a coating that turns black when an electrically heated pin is pressed against it. Thermal printers are durable, but thermal paper is sensitive to light, water, and heat, and the text and images produced by thermal printers can fade over time. They are faster and quieter than dot matrix printers. Although used in cash registers and ATMs, they aren't really useful for everyday printing Plotters A plotter is a special-purpose output device that draws images with ink pens. That is, the plotter is a graphics printer for making sophisticated graphs, charts, maps, and three-dimensional graphics as well as high-quality colored documents. It can also produce larger size of documents. Plotters require data in a vector graphics format that can produce images with a series of lines. Plotter is uses one or more pens that can be raised, lowered and moved over the printing media to draw graphics or text. Modern plotter usually uses only 4 pens (cyan, magenta, yellow and black). Electronic plotters do not use pens. It is widely used in scientific and engineering field like CAD (Computer Aided Design). There are two main types of plotters:
Drum Plotter: This is a plotter that has a drum. A paper wraps the drum that rotates to produce plots. Pens in a drum plotter move across the paper while the drum is turning. A drum plotter is usually used to produce smaller drawings.
Flatbed Plotter: This is a plotter that has a bed. This is also called a table plotter. The plotter draws graphics on the paper placed on the bed. There are several size of beds. This plotter is usually used for producing large drawings
Unit of Measurement of Storage and Memory Devices : BIT : is abbreviation of the words Binary Digit and is the smallest unit of information. It is either '0' or '1' . The raw data fed into computer is first converted into an electrical pulses or BITS, as computer only works on '0' & '1'. The '0' and '1' of the binary system corresponds to ON and OFF of the flow of electricity in the computer's circuits. Computers work by recognizing the presence or absence of an electrical pulses or BITS at particular time. Byte : is the measuring computer's memory and size of program. One Byte is the string of eight binary digits (BITS). It may represent a single letter, number or other characters. Computer memory is expressed in terms of KB, MB, GB, TB
Word: is the basic unit for accessing computer storage on a particular machine, usually the size of each instruction and the size of the data value which is most efficiently processed. The word on a PA-RISC machine is 32-bits (4 bytes), while a word on the Classic HP 3000 is 16-bits (2 bytes). A byte is 8 bits and 16-bits is called a halfword on PA-RISC machines. There are Machine Instructions to load and store words, halfwords, and bytes. Computer having smaller word length is slower than other having larger word length. Word length is generally fixed for a computer. Now-a-days computers have word length of 16, 32, 64,128 and even more bits.
CPU Speed : is measure in megahertz. A 1MHz CPU can accomplish one million CPU cycles (tasks) in one second. MIPS- short form of Millions of Instructions Per Second. The task execution speed of computer is also measured in terms of MIPS. Now a days computers come with CPU speed of GHz (gigahertz) For example CPU speed of 0.5 GHz =512 MHz= 512 MIPS i.e. 512,000,000 instructions per second.
nibble 4 bit (b)
byte (B) 8 bit (b)
kilobyte (KB) 1024 B
megabyte (MB) 1024 KB
gigabyte (GB) 1024 MB
terabyte (TB) 1024 GB
petabyte (PB) 1024 TB
exabyte (EB) 1024 PB
zettabyte (ZB) 1024 EB
yottabyte (YB) 1024 ZB
History of computer
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The term Computer is derived from Latin word "Computare" which means to calculate. So the history of computer begins with the development of calculating devices. Development of Calculating Devices :
Abacus:
Word Abacus comes to us by way of Latin as mutation of word abax.
One of the 1st mechanical device to calculation created by the Chinese about 3,000 BC and is generally seen in China, Japan and some other Asian countries.
Basically it consists of a rectangular frame carrying number of rods or wires. A centre bar divides these rods into 2 unequal parts. Upper smaller portion (Heaven) of each rod have 2 beads & on lower portion (Earth) have 5 beads.
Using Abacus one can add, subtract, multiply or divide.
Napier's bones:
John Napier, a Scottish mathematician invented a small instrument constructed of 10 rods called Napier's bones in 1617. Each rods were further divide into 9 diagonal numbered parts.
It enabled to carry out multiplication, division and roots faster
One had to take pencil and paper to get the result.
There rods were carved from bone.
In 1614 Napier 1st published the table of logarithms.
Slide Rule:
William Oughtred, an English mathematician constructed Slide rule in 1620. He used the principles of bones and logarithms. It has 2 movable graduated (scale marked on it) rulers kept slide by side.
Slide Rule is a mechanical analog computer. The slide rule is used primarily for multiplication and division, and also for functions such as roots, logarithms and trigonometry, but is not normally used for addition or subtraction.
Before the advent of the pocket calculator, it was the most commonly used calculation tool in science and engineering. It is considered as the 1st analog computing device.
Pascal's Calculator:
In 1642, the French mathematician and philosopher Blaise Pascal was credited for building first mechanical calculating device first called Arithmetic Machine, Pascal's Calculator and later Pascaline.
It could add and subtract directly and multiply and divide by repetition.
Machine consists of gears, 8 wheels and dials. Each wheel had 10 digits from (0 to 9).
It could add and subtract up to 9, 99, 99,999.
Difference and Analytical Engines: Charles Babbage an English mathematician known as father of computer. Charles Babbage invented 'Difference Engine' in1822.
A difference engine is an automatic, mechanical calculator designed to tabulate polynomial functions. The name derives from the method of divided differences, a way to tabulate functions by using a small set of polynomial coefficients. Both logarithmic and trigonometric functions, functions commonly used by both navigators and scientists, can be approximated by polynomials, so a difference engine can compute many useful sets of numbers
Large machine able to generate reliable astronomical and mathematical tables containing value accurate to 20 decimal place.
It was fully automatic in both calculating and printing output table. Project could not be completed due to lack of funds.
Analytical Engine'
The Analytical Engine was a proposed mechanical general-purpose computer designed by English mathematician Charles Babbage. It was first described in 1837 as the successor to Babbage's difference engine, a design for a mechanical calculator. The Analytical Engine
incorporated an arithmetical unit, control flow in the form of conditional branching and loops and integrated memory, making it the first Turing-complete (a system of data-manipulation rules ) design for a general-purpose computer.
A general- purpose, fully programmable automatic mechanical device.
It includes many features present in modern computer. For example: Input, output, storage, concept of using binary digits (bits).
Babbage was never able to complete construction of any of his machines due to conflicts with his chief engineer and inadequate funding. It was not until 100 years later, in the 1940s, that the first general-purpose computers were actually built.
Lady Augusta Ada Lovelace :
Augusta Ada, was an English writer mainly known for her work on Charles Babbage's early mechanical general-purpose computer, the analytical engine. Her notes on the engine include what is recognized as the first algorithm intended to be processed by a machine; thanks to this, she is sometimes considered the "World's First Computer Programmer". These notes contain what is considered the first computer program—that is, an algorithm encoded for processing by a machine. Though Babbage's engine has never been built, Lovelace's notes are important in the early history of computers. She also foresaw the capability of computers to go beyond mere calculating or number-crunching while others, including Babbage himself, focused only on these capabilities. US Defense Department named a programming language ADA in her honor.
MARK-I:
1st computer build by Howard Aiken of Harvard University. It was large electromechanical computer build in 1937, operational in 1944 and used until 1959. It was 51ft long, 8ft tall and 3ft wide having 18,000 vacuum tubes. It contains 7 lakhs 50 thousand parts and was strung with 500miles of wires. It weighed approximately 32 tons. Machine used instruction stored in paper and punched cards, handing 23 decimal place. Output was by card punch and electric typewriter.
1st electronic computer was Atanasoff-Berry computer (ABC) developed by John Vincent Atanasoff and Clifford Berry.
Computer Generation: The time of evolution of computer is divided into different generation by scientist's conference in 1962 on the basis of memory devices used in the computer. As memory device differs size, reliability, accuracy, cost etc. of computer. In The 1st Generation computer (1946-1958) Vacuum tubes were used as memory device. Vacuum tube is a set of metal electrodes and metal grids inside in a glass of metal tube which amplifies and switches in electric circuit. Vacuum tubes were developed by 'Lee Deforest' in 1908. Vacuum tubes consumed high power & generate large amount of heat. Vacuum tubes burned out easily & were hard to maintain. Machine level Language (0/1 binary digits) was used as programming language, which made extremely difficult & time consuming. Punch cards or paper was used for input & output of data.
Features : Relatively unreliable, extremely large, limited operating speed, very high system cost & working cost. Restricted to commercial & scientific application. 1st generation computers are ENIAC, EDVAC, EDSAC, UNIVAC-I, UNIVAC-II, MARK-II, PUNCH, IBM-650, IBM-702, IBM-704, IBM-705, IBM-709 etc.
In The 2nd Generation of computer:
(1959-1964) Transistors were used as memory device. Transistors shorts for transfer resister. A device composed of semiconductor materials that amplifies and switches in electric signals. It was developed by William B Shockley, John Burden and Walter Brattain in Bell labs in 1947. 1 transistor could do the task of 1000 vacuum tubes. It used less energy, faster and more reliable.
High level language and were introduced for programming which made programming easier. e.g. (FORTRAN, COBOL,BASIC etc)
Features : They were less expensive, smaller in size. Increase in storage capacity. Less power consumption and emitted less heat. Increase in operating speed. Punch cards and magnetic tape were used for input while punched cards and paper tape constituted the output.
Examples of 2nd Generation computer are: IMB 1620, IBM1401, LEO MARK-III, IBM-7050, DEC-1604, and RCA-501etc. In The 3rd generation of computer (1965-1974) Integrated circuit (IC) was used as memory device. Jack Kilby developed IC in 1958. IC is large number of electronic components placed on a single silicon chip.
Features : Monitors and keyboard were introduced for data output and input. Magnetic disks were used for auxiliary memory. Size of computer became much smaller. Reliability and accuracy improved. Include the use of operating system for automatic processing and multiprogramming
Example: IBM-360, IBM-370, UNIVAC110-8, UNIVAC-9000 4TH Generation of computer. (1975-1990) Very large scale Integration (VLSI) was as memory device VLSI squeezed hundreds of thousands of components onto a chip in the construction of computing elements. It's size about 0.5cm along one side and not more than 0.5cm thick
Features : Computers were highly reliable and accurate. Magnetic disk became the common source of external storage. Mouse, graphical user interface and handheld devices Micro computer were invented. Development of VLSI following by creation of micro-processor =50,000transition 1st microprocessor called Intel 4004 was developed by IBM in 1971.
Example: IBM, PC, Apple/Macintosh etc 5th Generation of computer (1991 & Beyond) ULSI or Biochips will be used as memory device. There computers will use super conductor technology Gallium Arsenide (GaAs ) Possibly be very small in size like micro-computer enable to use all facilities of super-computer. Cost of hardware and software will decrease. Computer will have artificial intelligence i.e. computer will understand human language, will speak command, understand problem, thinking like human. Knowledge based expert system, decentralized computing, parallel processing. Large uses of natural language processing and user friendly. Attempts are being made by Japan, German, and USA for the development of 5th Generation computer.
History of computer in Nepal: 2nd generation computer IBM-1401 was initially hired in rent by HMG, paying 1 lakh 25 thousand per month to use in census of year 2028 B.S. The machine took 1 year 7 month and 15 days for the processing of 1 crore 12.5 lakhs population. Another 4th generation British computer called ICL 2950/10 was purchased for the census of 2038 B.S. It was funded by UNDP and UNFPA ( 2 million American dollars). It took 1 year 3 month to complete census of 2038 B.S.
first generation computers :
The first generation computers were developed during 1943-1958. It used vacuum tubes as the active electronic components and was therefore very large. However some of the features are as follows- a) They were extremely large and occupied a very large space. b) They used vacuum tubes as memory device. c) They were very expensive and consumed a lot of electrical power. d) The operating speed was measured in milliseconds. e) These computers had low level of accuracy and reliability. f) Storage capacity was too small only 1 to 4Kb. g) They used machine level programming language. The examples are- UNIVAC, ENIAC, EDSAC, EDVAC, and UNIVAC. The second generation computers were developed during 1959-1965. The invention of the transistor by three scientists of Bell Telephone Laboratories in 1947 greatly changed the development of computers. However some of the features are as follows- a) These computers used transistor. b) They were smaller, faster and cheaper than first generation of computer. c) They consumed less electrical power than first generation. d) The operating speed was measured in microseconds. e) They were more reliable and accurate than the first generation computers. f) They could understand high level language such as COBOL. g) Magnetic tapes were used as secondary storage media. The examples are – IBM 1620, IBM 1401, and CDC 3600. The third generation computers were developed during 1966-1973. The development of Integrated Circuit (IC) signaled the beginning of the third generation computers. However some of the features are as follows- a) These computers used integrated circuits. b) They were small, efficient and reliable. c) Operating systems were developed. d) Monitors and keyboards were introduced for input and output of data. e) Magnetic disks were used for secondary storage. f) The operating speed was measured in nano seconds. g) They could understand large number of high level languages. The examples are – IBM 360, ICL -1900, and IBM 370 etc. The fourth generation computers were developed during 1974-1990. This generation of computer is presently in use. The development of microprocessor signaled the beginning of the fourth generation of computers. However some of the features are as follows- a) These computers use LSI and VLSI technologies. b) Its sizes were reduced to desktop and laptop computer. c) These computers are highly reliable and accurate. d) They have a large memory and high functional speed. e) The operating speed is measured in beyond picoseconds and MIPS (Million of instruction per second) f) Magnetic disk is the common source of external storage. g) Multiprocessing and multiprogramming OS (operating system) are used. h) 4GL are also used. The examples are – IBM PC, Apple/Macintosh, 8086, 80286 SX, 80386 SX etc. The computers having artificial intelligence (AI) and high processing capacity undergoing on the development stage from 1990 are said to be fifth generation computers. However some of the features are as follows- a) The speed will be extremely high in fifth generation computer. b) These computers will be using Ultra Large Scale Integration (ULSI) technology. c) The goal of fifth generation computers is to develop machines that will be able to think and take decisions. d) It can perform large number of parallel processing. e) Biochips and Gallium Arsenide (GaAS) will be used as memory devices. f) Large uses of natural language processing and user friendly.
first generation computers
first generation computers
Page5
ADVENT OF DIGITAL COMPUTER. ABC First Electronic computer was Atanasoff- berry computer (ABC) developed by John Vincent Atanasoff & Clifford Berry in 1937. It's weighed 750 lbs. It had memory storage of 3,000 bits(0.4Kb). Capacitors were used to store electrical charge that could represent number in form of logic 0s & logic1s. He used sparks to burn small spots onto the cards to store. Input was presented to machine in the form of punch cards.
ENIAC (Electronic Numerical Integrator and Calculator)
John William Mouchly & J.prelper Ecker Jr. constructed 1st general- purpose electronic computer in1946. This machine was built to meet the needs of the US Armed Forces. ENICA was 10ft tall, Occupied 1000 square feet of floor square weighed approximately 30 tons. It contained more than 70,000 resistors, 10,000 capaciotrs, 60,000 switches & 18,000 vacuums. The final machine consumed about 180,000 watts of electrical power. It is accepted as the 1st successful high- speed electronic digital computer & was used from 1946 to 1955.
EDSAC (Electronic Delay Storage Automatic Computer)
It was invented by Maurice Wilkes at Cambridge University England in May 1949. It was made up of 3,000 Vacuum tubes & used 30 kilowatts of electric power. Programs were input using paper tape & output result were printed on a teletype page printer. 1st operational stored- program computer.
UNIVAC-I (UNIVERSAL AUTOMATIC COMPUTER)
It was produced by John Mauchly & J.P. Eckert in 1951. It was based on EDSAC design. It was 8ft high, 15ft long & weighed 5 tons. Raw date was transcribed to magnetic tape by key to tape device. Date on punched cards was transcribed to magnetic tape with card to tape converter. Magnetic tape was principal input medium .Output was recorded on magnetic tape. 1st General purpose electronic digital computer designed for commercial use.
EDVAC (Electronic Discrete Variable Automatic Computer)
It was designed by John Mauchly & J.P.Eckert in 1952. It contained approx 4,000 Vacuum tube & 10,000 crystal diodes when it was finally completed. It was 2nd stored program computer.
The term Computer is derived from Latin word "Computare" which means to calculate. So the history of computer begins with the development of calculating devices. Development of Calculating Devices :
Abacus:
Word Abacus comes to us by way of Latin as mutation of word abax.
One of the 1st mechanical device to calculation created by the Chinese about 3,000 BC and is generally seen in China, Japan and some other Asian countries.
Basically it consists of a rectangular frame carrying number of rods or wires. A centre bar divides these rods into 2 unequal parts. Upper smaller portion (Heaven) of each rod have 2 beads & on lower portion (Earth) have 5 beads.
Using Abacus one can add, subtract, multiply or divide.
Napier's bones:
John Napier, a Scottish mathematician invented a small instrument constructed of 10 rods called Napier's bones in 1617. Each rods were further divide into 9 diagonal numbered parts.
It enabled to carry out multiplication, division and roots faster
One had to take pencil and paper to get the result.
There rods were carved from bone.
In 1614 Napier 1st published the table of logarithms.
Slide Rule:
William Oughtred, an English mathematician constructed Slide rule in 1620. He used the principles of bones and logarithms. It has 2 movable graduated (scale marked on it) rulers kept slide by side.
Slide Rule is a mechanical analog computer. The slide rule is used primarily for multiplication and division, and also for functions such as roots, logarithms and trigonometry, but is not normally used for addition or subtraction.
Before the advent of the pocket calculator, it was the most commonly used calculation tool in science and engineering. It is considered as the 1st analog computing device.
Pascal's Calculator:
In 1642, the French mathematician and philosopher Blaise Pascal was credited for building first mechanical calculating device first called Arithmetic Machine, Pascal's Calculator and later Pascaline.
It could add and subtract directly and multiply and divide by repetition.
Machine consists of gears, 8 wheels and dials. Each wheel had 10 digits from (0 to 9).
It could add and subtract up to 9, 99, 99,999.
Difference and Analytical Engines: Charles Babbage an English mathematician known as father of computer. Charles Babbage invented 'Difference Engine' in1822.
A difference engine is an automatic, mechanical calculator designed to tabulate polynomial functions. The name derives from the method of divided differences, a way to tabulate functions by using a small set of polynomial coefficients. Both logarithmic and trigonometric functions, functions commonly used by both navigators and scientists, can be approximated by polynomials, so a difference engine can compute many useful sets of numbers
Large machine able to generate reliable astronomical and mathematical tables containing value accurate to 20 decimal place.
It was fully automatic in both calculating and printing output table. Project could not be completed due to lack of funds.
Analytical Engine'
The Analytical Engine was a proposed mechanical general-purpose computer designed by English mathematician Charles Babbage. It was first described in 1837 as the successor to Babbage's difference engine, a design for a mechanical calculator. The Analytical Engine
incorporated an arithmetical unit, control flow in the form of conditional branching and loops and integrated memory, making it the first Turing-complete (a system of data-manipulation rules ) design for a general-purpose computer.
A general- purpose, fully programmable automatic mechanical device.
It includes many features present in modern computer. For example: Input, output, storage, concept of using binary digits (bits).
Babbage was never able to complete construction of any of his machines due to conflicts with his chief engineer and inadequate funding. It was not until 100 years later, in the 1940s, that the first general-purpose computers were actually built.
Lady Augusta Ada Lovelace :
Augusta Ada, was an English writer mainly known for her work on Charles Babbage's early mechanical general-purpose computer, the analytical engine. Her notes on the engine include what is recognized as the first algorithm intended to be processed by a machine; thanks to this, she is sometimes considered the "World's First Computer Programmer". These notes contain what is considered the first computer program—that is, an algorithm encoded for processing by a machine. Though Babbage's engine has never been built, Lovelace's notes are important in the early history of computers. She also foresaw the capability of computers to go beyond mere calculating or number-crunching while others, including Babbage himself, focused only on these capabilities. US Defense Department named a programming language ADA in her honor.
MARK-I:
1st computer build by Howard Aiken of Harvard University. It was large electromechanical computer build in 1937, operational in 1944 and used until 1959. It was 51ft long, 8ft tall and 3ft wide having 18,000 vacuum tubes. It contains 7 lakhs 50 thousand parts and was strung with 500miles of wires. It weighed approximately 32 tons. Machine used instruction stored in paper and punched cards, handing 23 decimal place. Output was by card punch and electric typewriter.
1st electronic computer was Atanasoff-Berry computer (ABC) developed by John Vincent Atanasoff and Clifford Berry.
Computer Generation: The time of evolution of computer is divided into different generation by scientist's conference in 1962 on the basis of memory devices used in the computer. As memory device differs size, reliability, accuracy, cost etc. of computer. In The 1st Generation computer (1946-1958) Vacuum tubes were used as memory device. Vacuum tube is a set of metal electrodes and metal grids inside in a glass of metal tube which amplifies and switches in electric circuit. Vacuum tubes were developed by 'Lee Deforest' in 1908. Vacuum tubes consumed high power & generate large amount of heat. Vacuum tubes burned out easily & were hard to maintain. Machine level Language (0/1 binary digits) was used as programming language, which made extremely difficult & time consuming. Punch cards or paper was used for input & output of data.
Features : Relatively unreliable, extremely large, limited operating speed, very high system cost & working cost. Restricted to commercial & scientific application. 1st generation computers are ENIAC, EDVAC, EDSAC, UNIVAC-I, UNIVAC-II, MARK-II, PUNCH, IBM-650, IBM-702, IBM-704, IBM-705, IBM-709 etc.
In The 2nd Generation of computer:
(1959-1964) Transistors were used as memory device. Transistors shorts for transfer resister. A device composed of semiconductor materials that amplifies and switches in electric signals. It was developed by William B Shockley, John Burden and Walter Brattain in Bell labs in 1947. 1 transistor could do the task of 1000 vacuum tubes. It used less energy, faster and more reliable.
High level language and were introduced for programming which made programming easier. e.g. (FORTRAN, COBOL,BASIC etc)
Features : They were less expensive, smaller in size. Increase in storage capacity. Less power consumption and emitted less heat. Increase in operating speed. Punch cards and magnetic tape were used for input while punched cards and paper tape constituted the output.
Examples of 2nd Generation computer are: IMB 1620, IBM1401, LEO MARK-III, IBM-7050, DEC-1604, and RCA-501etc. In The 3rd generation of computer (1965-1974) Integrated circuit (IC) was used as memory device. Jack Kilby developed IC in 1958. IC is large number of electronic components placed on a single silicon chip.
Features : Monitors and keyboard were introduced for data output and input. Magnetic disks were used for auxiliary memory. Size of computer became much smaller. Reliability and accuracy improved. Include the use of operating system for automatic processing and multiprogramming
Example: IBM-360, IBM-370, UNIVAC110-8, UNIVAC-9000 4TH Generation of computer. (1975-1990) Very large scale Integration (VLSI) was as memory device VLSI squeezed hundreds of thousands of components onto a chip in the construction of computing elements. It's size about 0.5cm along one side and not more than 0.5cm thick
Features : Computers were highly reliable and accurate. Magnetic disk became the common source of external storage. Mouse, graphical user interface and handheld devices Micro computer were invented. Development of VLSI following by creation of micro-processor =50,000transition 1st microprocessor called Intel 4004 was developed by IBM in 1971.
Example: IBM, PC, Apple/Macintosh etc 5th Generation of computer (1991 & Beyond) ULSI or Biochips will be used as memory device. There computers will use super conductor technology Gallium Arsenide (GaAs ) Possibly be very small in size like micro-computer enable to use all facilities of super-computer. Cost of hardware and software will decrease. Computer will have artificial intelligence i.e. computer will understand human language, will speak command, understand problem, thinking like human. Knowledge based expert system, decentralized computing, parallel processing. Large uses of natural language processing and user friendly. Attempts are being made by Japan, German, and USA for the development of 5th Generation computer.
History of computer in Nepal: 2nd generation computer IBM-1401 was initially hired in rent by HMG, paying 1 lakh 25 thousand per month to use in census of year 2028 B.S. The machine took 1 year 7 month and 15 days for the processing of 1 crore 12.5 lakhs population. Another 4th generation British computer called ICL 2950/10 was purchased for the census of 2038 B.S. It was funded by UNDP and UNFPA ( 2 million American dollars). It took 1 year 3 month to complete census of 2038 B.S.
first generation computers :
The first generation computers were developed during 1943-1958. It used vacuum tubes as the active electronic components and was therefore very large. However some of the features are as follows- a) They were extremely large and occupied a very large space. b) They used vacuum tubes as memory device. c) They were very expensive and consumed a lot of electrical power. d) The operating speed was measured in milliseconds. e) These computers had low level of accuracy and reliability. f) Storage capacity was too small only 1 to 4Kb. g) They used machine level programming language. The examples are- UNIVAC, ENIAC, EDSAC, EDVAC, and UNIVAC. The second generation computers were developed during 1959-1965. The invention of the transistor by three scientists of Bell Telephone Laboratories in 1947 greatly changed the development of computers. However some of the features are as follows- a) These computers used transistor. b) They were smaller, faster and cheaper than first generation of computer. c) They consumed less electrical power than first generation. d) The operating speed was measured in microseconds. e) They were more reliable and accurate than the first generation computers. f) They could understand high level language such as COBOL. g) Magnetic tapes were used as secondary storage media. The examples are – IBM 1620, IBM 1401, and CDC 3600. The third generation computers were developed during 1966-1973. The development of Integrated Circuit (IC) signaled the beginning of the third generation computers. However some of the features are as follows- a) These computers used integrated circuits. b) They were small, efficient and reliable. c) Operating systems were developed. d) Monitors and keyboards were introduced for input and output of data. e) Magnetic disks were used for secondary storage. f) The operating speed was measured in nano seconds. g) They could understand large number of high level languages. The examples are – IBM 360, ICL -1900, and IBM 370 etc. The fourth generation computers were developed during 1974-1990. This generation of computer is presently in use. The development of microprocessor signaled the beginning of the fourth generation of computers. However some of the features are as follows- a) These computers use LSI and VLSI technologies. b) Its sizes were reduced to desktop and laptop computer. c) These computers are highly reliable and accurate. d) They have a large memory and high functional speed. e) The operating speed is measured in beyond picoseconds and MIPS (Million of instruction per second) f) Magnetic disk is the common source of external storage. g) Multiprocessing and multiprogramming OS (operating system) are used. h) 4GL are also used. The examples are – IBM PC, Apple/Macintosh, 8086, 80286 SX, 80386 SX etc. The computers having artificial intelligence (AI) and high processing capacity undergoing on the development stage from 1990 are said to be fifth generation computers. However some of the features are as follows- a) The speed will be extremely high in fifth generation computer. b) These computers will be using Ultra Large Scale Integration (ULSI) technology. c) The goal of fifth generation computers is to develop machines that will be able to think and take decisions. d) It can perform large number of parallel processing. e) Biochips and Gallium Arsenide (GaAS) will be used as memory devices. f) Large uses of natural language processing and user friendly.
first generation computers
first generation computers
Page5
ADVENT OF DIGITAL COMPUTER. ABC First Electronic computer was Atanasoff- berry computer (ABC) developed by John Vincent Atanasoff & Clifford Berry in 1937. It's weighed 750 lbs. It had memory storage of 3,000 bits(0.4Kb). Capacitors were used to store electrical charge that could represent number in form of logic 0s & logic1s. He used sparks to burn small spots onto the cards to store. Input was presented to machine in the form of punch cards.
ENIAC (Electronic Numerical Integrator and Calculator)
John William Mouchly & J.prelper Ecker Jr. constructed 1st general- purpose electronic computer in1946. This machine was built to meet the needs of the US Armed Forces. ENICA was 10ft tall, Occupied 1000 square feet of floor square weighed approximately 30 tons. It contained more than 70,000 resistors, 10,000 capaciotrs, 60,000 switches & 18,000 vacuums. The final machine consumed about 180,000 watts of electrical power. It is accepted as the 1st successful high- speed electronic digital computer & was used from 1946 to 1955.
EDSAC (Electronic Delay Storage Automatic Computer)
It was invented by Maurice Wilkes at Cambridge University England in May 1949. It was made up of 3,000 Vacuum tubes & used 30 kilowatts of electric power. Programs were input using paper tape & output result were printed on a teletype page printer. 1st operational stored- program computer.
UNIVAC-I (UNIVERSAL AUTOMATIC COMPUTER)
It was produced by John Mauchly & J.P. Eckert in 1951. It was based on EDSAC design. It was 8ft high, 15ft long & weighed 5 tons. Raw date was transcribed to magnetic tape by key to tape device. Date on punched cards was transcribed to magnetic tape with card to tape converter. Magnetic tape was principal input medium .Output was recorded on magnetic tape. 1st General purpose electronic digital computer designed for commercial use.
EDVAC (Electronic Discrete Variable Automatic Computer)
It was designed by John Mauchly & J.P.Eckert in 1952. It contained approx 4,000 Vacuum tube & 10,000 crystal diodes when it was finally completed. It was 2nd stored program computer.