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2009-11-23T21:49:00.000-08:00

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2009-11-16T06:26:00.000-08:00

2009-11-03T21:30:00.000-08:00

Line Printer, in computer science, any printer that prints one line at a time, as opposed to one character at a time (as with a standard dot-matrix printer) or one page at a time (as with a laser printer).

Line printers typically produce the 11-by-17-inch “computer” printouts familiar to many. They are high-speed devices and are often used with mainframes, minicomputers, or networked machines rather than with single-user systems. Types of line printers include chain printers and band printers. The abbreviation LPT originally stood for “line printer”; on MS-DOS microcomputers, the same abbreviation is used for the computer's parallel output port(s).

Laser Printer,

2009-11-02T21:16:00.000-08:00

Laser Printer, an electrophotographic printer that is based on the technology used by photocopiers. A focused laser beam and a rotating mirror are used to draw an image of the desired page on a photosensitive drum.

This image is converted on the drum into an electrostatic charge, which attracts and holds toner. A piece of electrostatically charged paper is rolled against the drum, which pulls the toner away from the drum and onto the paper. Heat is then applied to fuse the toner to the paper.

Finally, the electrical charge is removed from the drum and the excess toner is collected. By omitting this final step and repeating only the toner-application and paper-handling steps, the printer can make multiple copies.

The only serious drawback of a laser printer is that it offers less paper-handling flexibility than do dot-matrix printers. Both multipart forms and wide-carriage printing, for example, are better handled by dot-matrix or daisy-wheel printers.

Inkjet printer,

2009-11-01T21:05:00.000-08:00

Printer, a computerperipheral that puts text or a computer-generated image on paper or on another medium, such as a transparency. Printers can be categorized in any of several ways. The most common distinction is impact vs. nonimpact. Impact printers physically strike the paper and are exemplified by pin dot-matrix printers and daisy-wheel printers; nonimpact printers include every other type of print mechanism, including laser, ink-jet, and thermal printers. Other possible methods of categorizing printers include (but are not limited to) the following:

Print technology: Chief among these, with microcomputers, are pin dot-matrix, ink-jet, laser, thermal, and (although somewhat outdated) daisy-wheel or thimble printers. Pin dot-matrix printers can be further classified by the number of pins in the print head: 9, 18, 24, and so on.

Character formation: Fully formed characters made of continuous lines (for example, those produced by a daisy-wheel printer) vs. dot-matrix characters composed of patterns of dots (such as those produced by standard dot-matrix, ink-jet, and thermal printers). Laser printers, while technically dot-matrix, are generally considered to produce fully formed characters because their output is very clear and the dots are extremely small and closely spaced.

Method of transmission: parallel (byte-by-byte transmission) vs. serial (bit-by-bit transmission). These categories refer to the means by which output is sent to the printer rather than to any mechanical distinctions. Many printers are available in either serial or parallel versions, and still other printers offer both choices, yielding greater flexibility in installation options.

Method of printing: Character by character, line by line, or page by page. Character printers include standard dot-matrix, ink-jet, thermal, and daisy-wheel printers. Line printers include the band, chain, and drum printers that are commonly associated with large computer installations or networks. Page printers include the electrophotographic printers, such as laser printers.

Print capability: Text-only vs. text-and-graphics. Text-only printers, including most daisy-wheel and thimble printers and some dot-matrix and laser printers, can reproduce only characters for which they have matching patterns, such as embossed type, or internal character maps. Text-and-graphics printers—dot-matrix, ink-jet, laser, and others—can reproduce all manner of images by “drawing” each as a pattern of dots.

The CPU

2009-11-01T19:01:00.000-08:00

Information from an input device or from the computer’s memory is communicated via the bus to the central processing unit (CPU), which is the part of the computer that translates commands and runs programs. The CPU is a microprocessor chip—that is, a single piece of silicon containing millions of tiny, microscopically wired electrical components. Information is stored in a CPU memory location called a register. Registers can be thought of as the CPU’s tiny scratchpad,

temporarily storing instructions or data. When a program is running, one special register called the program counter keeps track of which program instruction comes next by maintaining the memory location of the next program instruction to be executed. The CPU’s control unit coordinates and times the CPU’s functions, and it uses the program counter to locate and retrieve the next instruction from memory.

In a typical sequence, the CPU locates the next instruction in the appropriate memory device. The instruction then travels along the bus from the computer’s memory to the CPU, where it is stored in a special instruction register. Meanwhile, the program counter changes—usually increasing a small amount—so that it contains the location of the instruction that will be executed next. The current instruction is analyzed by a decoder, which determines what the instruction will do. Any data the instruction needs are retrieved via the bus and placed in the CPU’s registers. The CPU executes the instruction, and the results are stored in another register or copied to specific memory locations via a bus. This entire sequence of steps is called an instruction cycle. Frequently, several instructions may be in process simultaneously, each at a different stage in its instruction cycle. This is called pipeline processing.

Monitor,

2009-10-30T19:50:00.000-07:00

Monitor, in computer science, device connected to a computer that displays information on a screen. Modern computer monitors can display a wide variety of information, including text, icons (pictures representing commands), photographs, computer rendered graphics, video, and animation.

Most computer monitors use a cathode-ray tube (CRT) as the display device. A CRT is a glass tube that is narrow at one end and opens to a flat screen at the other end. The CRTs used for monitors have rectangular screens, but other types of CRTs may have circular or square screens. The narrow end of the CRT contains a single electron gun for a monochrome, or single-color monitor, and three electron guns for a color monitor—one electron gun for each of the three primary colors: red, green, and yellow. The display screen is covered with tiny phosphor dots that emit light when struck by electrons from an electron gun.

Monochrome monitors have only one type of phosphor dot while color monitors have three types of phosphor dots, each emitting either red, green, or blue light. One red, one green, and one blue phosphor dot are grouped together into a single unit called a picture element, or pixel. A pixel is the smallest unit that can be displayed on the screen. Pixels are arranged together in rows and columns and are small enough that they appear connected and continuous to the eye.

Electronic circuitry within the monitor controls an electromagnet that scans and focuses electron beams onto the display screen, illuminating the pixels. Image intensity is controlled by the number of electrons that hit a particular pixel. The more electrons that hit a pixel, the more light the pixel emits. The pixels, illuminated by each pass of the beams, create images on the screen. Variety of color and shading in an image is produced by carefully controlling the intensity of the electron beams hitting each of the dots that make up the pixels. The speed at which the electron beams repeat a single scan over the pixels is known as the refresh rate. Refresh rates are usually about 60 times a second.

Monochrome monitors display one color for text and pictures, such as white, green, or amber, against a dark color, such as black, for the background. Gray-scale monitors are a type of monochrome monitor that can display between 16 and 256 different shades of gray.

Manufacturers describe the quality of a monitor’s display by dot pitch, which is the amount of space between the centers of adjacent pixels. Smaller dot pitches mean the pixels are more closely spaced and the monitor will yield sharper images. Most monitors have dot pitches that range from 0.22 mm (0.008 in) to 0.39 mm (0.015 in).

The screen size of monitors is measured by the distance from one corner of the display to the diagonally opposite corner. A typical size is 38 cm (15 in), with most monitors ranging in size from 22.9 cm (9 in) to 53 cm (21 in). Standard monitors are wider than they are tall and are called landscape monitors. Monitors that have greater height than width are called portrait monitors.

The amount of detail, or resolution, that a monitor can display depends on the size of the screen, the dot pitch, and on the type of display adapter used. The display adapter is a circuit board that receives formatted information from the computer and then draws an image on the monitor, displaying the information to the user. Display adapters follow various standards governing the amount of resolution they can obtain. Most color monitors are compatible with Video Graphics Array (VGA) standards, which are 640 by 480 pixels (640 pixels on each of 480 rows), or about 300,000 pixels. VGA yields 16 colors, but most modern monitors display far more colors and are considered high resolution in comparison. Super VGA (SVGA) monitors have 1024 by 768 pixels (about 800,000) and are capable of displaying more than 60,000 different colors. Some SVGA monitors can display more than 16 million different colors.

A monitor is one type of computer display, defined by its CRT screen. Other types of displays include flat, laptop computer screens that often use liquid-crystal displays (LCDs). Other thin, flat-screen monitors that do not employ CRTs are currently being developed.

Microphone,

2009-10-29T05:59:00.000-07:00

Microphone, device used to transform sound energy into electrical energy (see Sound Recording and Reproduction). Microphones are important in many kinds of communications systems and in instruments that measure sound and noise. The American inventor Alexander Graham Bell built the first microphone in 1876 when he constructed his telephone transmitter.

The simplest type of modern microphone is the carbon microphone, used in telephones. This microphone consists of a metallic cup filled with carbon granules; a movable metallic diaphragm mounted in contact with the granules covers the open end of the cup. Wires attached to the cup and diaphragm are connected to an electrical circuit so that a current flows through the carbon granules. Sound waves vibrate the diaphragm, varying the pressure on the carbon granules. The electrical resistance of the carbon granules changes with the varying pressure, causing the current in the circuit to change according to the vibrations of the diaphragm. The varying current may either actuate a nearby telephone receiver or may be amplified and transmitted to a distant receiver. If the current variation is suitably amplified, it may also be used to modulate a radio transmitter.

Another common type, the crystal microphone, utilizes piezoelectric crystals, in which a voltage develops between two faces of the crystal when pressure is applied to the crystal (see Piezoelectric Effect). In this microphone sound waves vibrate a diaphragm, which in turn varies the pressure on a piezoelectric crystal. This generates a small voltage, which is then amplified.

Examples of dynamic microphones include ribbon microphones and moving-coil microphones. In ribbon microphones, a thin metallic ribbon is attached to the diaphragm and placed in a magnetic field. When sound waves strike the diaphragm and vibrate the ribbon, a small voltage is generated in the ribbon by electromagnetic induction. A moving-coil microphone operates on essentially the same principle but has a coil of light wire, instead of a ribbon, attached to the diaphragm. Some modern microphones, designed to pick up sound from one direction only, combine both ribbon and coil elements.
Another type of microphone is the condenser microphone. The condenser microphone has two thin metallic plates placed close to each other that serve as a capacitor. The back plate of the capacitor is fixed, and the front plate serves as the diaphragm. Sound waves alter the spacing between the plates, changing the electrical capacitance between them. By placing such a microphone in a suitable circuit, these variations may be amplified, producing an electrical signal. Condenser microphones can be very small. A common type of condenser microphone, the electret condenser microphone, is used in hearing aids.

Among the important characteristics of microphones are their frequency response, directionality, sensitivity, and immunity to outside disturbances such as shock or vibration.

Mouse,

2009-10-28T05:21:00.000-07:00

Mouse (computer), a common pointing device, popularized by

its inclusion as standard equipment with the Apple Macintosh. With the rise in popularity of graphical user interfaces (Graphical User Interface) in MS-DOS; UNIX, and OS/2, use of mice is growing throughout the personal computer and workstation worlds.

The basic features of a mouse are a casing with a flat bottom, designed to be gripped by one hand; one or more buttons on the top; a multidirectional detection device (usually a ball) on the bottom; and a cable connecting the mouse to the computer.

See the illustration.

By moving the mouse on a surface (such as a desk), the user typically controls an on-screen cursor. A mouse is a relative pointing device because there are no defined limits to the mouse's movement and because its placement on a surface does not map directly to a specific screen location.

To select items or choose commands on the screen, the user presses one of the mouse's buttons, producing a “mouse click.”

Analog Modem,

2009-10-27T05:19:00.000-07:00

An analog modem converts the digital signals of the sending computer to analog signals

that can be transmitted through telephone lines. When the signal reaches its destination, another modem reconstructs the original digital signal, which is processed by the receiving computer. A standard analog modem has a maximum speed of 33.6 Kbps.

The word modem is an acronym formed from the two basic functions of an analog modem: modulation and demodulation. To convert a digital signal to an analog one, the modem generates a carrier wave and modulates, or adjusts, it according to the digital signal. The kind of modulation used depends on the application and the speed of operation for which the modem is designed. For example, many high-speed modems use a combination of amplitude modulation, in which the amplitude (see Wave Motion) of the carrier wave is changed to encode the digital information, and phase modulation, in which the phase of the carrier wave is changed to encode the digital information. The process of receiving the analog signal and converting it back to a digital signal is called demodulation.

Cable modem,

2009-10-26T05:17:00.000-07:00

Cable modems permit the transmission of data over community antenna television (CATV) networks—that is, the network of cables used to distribute cable television. A cable modem transmits data from the network at about 3 Mbps and transmits data to the network at between 500 Kbps and 2.5 Mbps.

Like a standard analog modem, a cable modem converts between a digital signal and an analog signal.

Cable modems are much more complex than standard analog modems. They also incorporate a tuner that separates the digital data from the rest of the broadcast television signal. Because users in multiple locations share the same cable, the modem also includes hardware that permits multiple connections and an encryption/decryption device that prevents data from being intercepted by another user or being sent to the wrong place.

Random Access Memory, ( RAM )

2009-10-25T19:08:00.001-07:00

Random access memory is also called main memory because it is the primary memory that the CPU uses when processing information.

The electronic circuits used to construct this main internal RAM can be classified as dynamic RAM (DRAM), synchronized dynamic RAM (SDRAM), or static RAM (SRAM). DRAM, SDRAM, and SRAM all involve different ways of using transistors and capacitors to store data. In DRAM or SDRAM, the circuit for each bit consists of a transistor, which acts as a switch, and a capacitor, a device that can store a charge.

To store the binary value 1 in a bit, DRAM places an electric charge on the capacitor.To store the binary value 0, DRAM removes all electric charge from the capacitor.The transistor is used to switch the charge onto the capacitor.

When it is turned on, the transistor acts like a closed switch that allows electric current to flow into the capacitor and build up a charge.The transistor is then turned off, meaning that it acts like an open switch, leaving the charge on the capacitor.To store a 0, the charge is drained from the capacitor while the transistor is on, and then the transistor is turned off, leaving the capacitor uncharged.To read a value in a DRAM bit location, a detector circuit determines whether a charge is present or absent on the relevant capacitor.DRAM is called dynamic because it is continually refreshed.
The memory chips themselves cannot hold values over long periods of time. Because capacitors are imperfect, the charge slowly leaks out of them, which results in loss of the stored data. Thus, a DRAM memory system contains additional circuitry that periodically reads and rewrites each data value. This replaces the charge on the capacitors, a process known as refreshing memory. The major difference between SDRAM and DRAM arises from the way in which refresh circuitry is created. DRAM contains separate, independent circuitry to refresh memory. The refresh circuitry in SDRAM is synchronized to use the same hardware clock as the CPU. The hardware clock sends a constant stream of pulses through the CPU’s circuitry. Synchronizing the refresh circuitry with the hardware clock results in less duplication of electronics and better access coordination between the CPU and the refresh circuits.

In SRAM, the circuit for a bit consists of multiple transistors that hold the stored value without the need for refresh. The chief advantage of SRAM lies in its speed. A computer can access data in SRAM more quickly than it can access data in DRAM or SDRAM. However, the SRAM circuitry draws more power and generates more heat than DRAM or SDRAM. The circuitry for a SRAM bit is also larger, which means that a SRAM memory chip holds fewer bits than a DRAM chip of the same size. Therefore, SRAM is used when access speed is more important than large memory capacity or low power consumption.

The time it takes the CPU to transfer data to or from memory is particularly important because it determines the overall performance of the computer. The time required to read or write one bit is known as the memory access time. Current DRAM and SDRAM access times are between 30 and 80 nanoseconds (billionths of a second). SRAM access times are typically four times faster than DRAM.

The internal RAM on a computer is divided into locations, each of which has a unique numerical address associated with it. In some computers a memory address refers directly to a single byte in memory, while in others, an address specifies a group of four bytes called a word. Computers also exist in which a word consists of two or eight bytes, or in which a byte consists of six or ten bits.

When a computer performs an arithmetic operation, such as addition or multiplication, the numbers used in the operation can be found in memory. The instruction code that tells the computer which operation to perform also specifies which memory address or addresses to access. An address is sent from the CPU to the main memory (RAM) over a set of wires called an address bus. Control circuits in the memory use the address to select the bits at the specified location in RAM and send a copy of the data back to the CPU over another set of wires called a data bus.

Inside the CPU, the data passes through circuits called the data path to theircuits that perform the arithmetic operation. The exact details depend on the model of the CPU. For example, some CPUs use an intermediate step in which the data is first loaded into a high-speed memory device within the CPU called a register.

Modem,

2009-10-25T05:12:00.000-07:00

Modem, device that enables computers, facsimile machines, and other equipment to communicate with each other across telephone lines or over cable television network cables. In the strictest sense, a modem is a device that converts between analog signals, such as sound waves, and digital signals, which are used by computers. However, the term has also come to include devices that permit the transmission of entirely digital signals.
Modems transmit data at different speeds, measured by the number of bits of data,

they send per second (bps). A 28.8 Kbps modem sends data at 28,800 bits per second. A 56 Kbps modem is twice as fast, sending and receiving data at a rate of 56,000 bits per second.

Scanner,

2009-10-24T05:09:00.000-07:00

Optical Scanner, a computer input device (see Input/Output Device) that uses light-sensing equipment

to scan paper or another medium, translating the pattern of light and dark (or color) into a digital signal that can be manipulated by either optical character recognition software or graphics software. A frequently encountered type of scanner is “flatbed,” meaning that the scanning device moves across or reads across a stationary document.

On a flatbed scanner such as the common office copier, such objects are placed face down on a flat piece of glass and scanned by a mechanism that passes under them. Another type of flatbed scanner uses a scanning element placed in a stationary housing above the document.

Other scanners work by pulling in sheets of paper, which are scanned as they pass over a stationary scanning mechanism, as in the common office fax machine. Some specialized scanners work with a standard video camera, translating the video signal into a digital signal for processing by computer software.A very popular type of scanner is the hand-held scanner, so called because the user holds the scanner in his or her hand and moves it over the document to be scanned. Hand-held scanners have the advantage of relatively low cost; however, they are somewhat limited by their inability to scan areas more than a few inches wide.

Keyboard,

2009-10-23T05:03:00.000-07:00

Keyboard, in computer science, a keypad device with buttons or keys that a user presses to enter data characters and commands into a computer. Keyboards emerged from the combination of typewriter and computer-terminal technology. They are one of the fundamental pieces of personal computer (PC) hardware, along with the central processing unit (CPU), the monitor or screen, and the mouse or other cursor device.
The most common English-language key pattern for typewriters and keyboards is called QWERTY, after the layout of the first six letters in the top row of its keys (from left to right).

In the late 1860s, American inventor and printer Christopher Sholes invented the modern form of the typewriter. Sholes created the QWERTY keyboard layout by separating commonly used letters so that typists would type slower and not jam their mechanical typewriters. Subsequent generations of typists have learned to type using QWERTY keyboards, prompting manufacturers to maintain this key orientation on typewriters.

Computer keyboards copied the QWERTY key layout and have followed the precedent set by typewriter manufacturers of keeping this convention. Modern keyboards connect with the computer CPU by cable or by infrared transmitter. When a key on the keyboard is pressed, a numeric code is sent to the keyboard’s driver software and to the computer’s operating system software. The driver translates this data into a specialized command that the computer’s CPU and application programs understand. In this way, users may enter text, commands, numbers, or other data. The term character is generally reserved for letters, numbers, and punctuation, but may also include control codes, graphical symbols, mathematical symbols, and graphic images.Almost all standard English-language keyboards have keys for each character of the American Standard Code for Information Interchange (ASCII) character set, as well as various function keys. Most computers and applications today use seven or eight data bits for each character. Other character sets include ISO Latin 1, Kanji, and Unicode. Each character is represented by a unique number understood by the computer. For example, ASCII code 65 is equal to the letter A. The function keys generate short, fixed sequences of character codes that instruct application programs running on the computer to perform certain actions. Often, keyboards also have directional buttons for moving the screen cursor, separate numeric pads for entering numeric and arithmetic data, and a switch for turning the computer on and off. Some keyboards, including most for laptop computers, also incorporate a trackball, mouse pad, or other cursor-directing device. No standard exists for positioning the function, numeric, and other buttons on a keyboard relative to the QWERTY and other typewriting keys. Thus layouts vary on keyboards.
An alternative keyboard design not yet widely used but broadly acknowledged for its speed advantages is the Dvorak keyboard. In the 1930s, American educators August Dvorak and William Dealy designed this key set so that the letters that make up most words in the English language are in the middle row of keys and are easily reachable by a typist’s fingers. Common letter combinations are also positioned so that they can be typed quickly. Most keyboards are arranged in rectangles, left to right around the QWERTY layout. Newer, innovative keyboard designs are more ergonomic in shape. These keyboards have separated banks of keys and are less likely to cause carpal tunnel syndrome, a disorder often caused by excessive typing on less ergonomic keyboards.

Dot Matrix Printer,

2009-10-22T06:40:00.000-07:00

Dot-Matrix Printer, in computer science, any printer that produces characters made up of dots using a wire-pin print head.

The quality of output from a dot-matrix printer depends largely on the number of dots in the matrix, which might be low enough to show individual dots or might be high enough to approach the look of fully formed characters. Dot-matrix printers are often categorized by the number of pins in the print head—typically 9, 18, or 24.

Joystick

2009-10-22T05:01:00.000-07:00

Joystick, in computer science, a popular pointing device, used mostly for playing computer games but used for other tasks as well. A joystick usually has a square or rectangular plastic base to which is attached a vertical stem. Control buttons are located on the base and sometimes on top of the stem. The stem can be moved omnidirectionally to control the movement of an object on the screen.

The buttons activate various software features, generally producing on-screen events. A joystick is usually a relative pointing device, moving an object on the screen when the stem is moved from the center and stopping the movement when the stem is released. In industrial control applications, the joystick can also be an absolute pointing device, with each position of the stem mapped to a specific on-screen location.

Light pen,

2009-10-21T06:05:00.001-07:00

Light Pen, a pointing device in which the user holds a wand, which is attached to the computer, up to the screen and selects items or chooses commands on the screen (the equivalent of a mouse click) either by pressing a clip on the side of the light pen or by pressing the light pen against the surface of the screen.

The wand contains light sensors and sends a signal to the computer whenever it records a light, as during close contact with the screen when the non-black pixels beneath the wand's tip are refreshed by the display's electron beam. The computer's screen is not all lit at once—the electron beam that lights pixels on the screen traces across the screen row by row, all in the space of 1/60 of a second.

By noting exactly when the light pen detected the electron beam passing its tip, the computer can determine the light pen's location on the screen. The light pen doesn't require a special screen or screen coating, as does a touch screen, but its disadvantage is that holding the pen up for an extended length of time is tiring to the user.

Digital Camera

2009-10-21T04:54:00.000-07:00

Digital cameras are now available for both professional photographers and amateur enthusiasts. The more expensive professional cameras function as sophisticated 35-millimeter cameras but record the picture information as pixels, or digital dots of color (see Computer Graphics).

There can be several million pixels in a high-resolution, full-color digital photograph. Some digital cameras are able to transfer their large picture files directly into a computer for storage. Others accept a disc or similar portable storage unit to achieve the same purpose. The original high-resolution image can later be reproduced in ink (in a magazine, for example) or as a conventional silver halide print.

Digital cameras aimed at the amateur photography market function much as point-and-shoot cameras do, with automatic focus, automatic exposure, and built-in electronic flash. Pictures from these cameras contain fewer pixels than those from a more expensive camera and are therefore not as sharp. After taking pictures, the user can connect the camera directly to a television set or video cassette recorder, so the whole family can look at snapshots together. Alternatively, image files can be transferred to a home computer, stored on disks, or sent to friends via electronic mail.

FORTRAN

2009-09-18T01:54:00.000-07:00

From 1954 to 1958 American computer scientist John Backus of International Business Machines, Inc. (IBM) developed Fortran, an acronym for Formula Translation. It became a standard programming language because it could process mathematical formulas. Fortran and its variations are still in use today, especially in physics.

Operating System

2009-09-16T09:00:00.000-07:00

It is an interface between user and the computer machine.

Operating System (OS), in computer science, the basic software that controls a computer. The operating system has three major functions: It coordinates and manipulates computer hardware, such as computer memory, printers, disks, keyboard, mouse, and monitor;

it organizes files on a variety of storage media, such as floppy disk, hard drive, compact disc, digital video disc, and tape; and it manages hardware errors and the loss of data.

When a computer is turned on it searches for instructions in its memory. These instructions tell the computer how to start up. Usually, one of the first sets of these instructions is a special program called the operating system, which is the software that makes the computer work. It prompts the user (or other machines) for input and commands, reports the results of these commands and other operations, stores and manages data, and controls the sequence of the software and hardware actions. When the user requests that a program run, the operating system loads the program in the computer’s memory and runs the program. Popular operating systems, such as Microsoft Windows and the Macintosh system (Mac OS), have graphical user interfaces (GUIs)—that use tiny pictures, or icons, to represent various files and commands. To access these files or commands, the user clicks the mouse on the icon or presses a combination of keys on the keyboard. Some operating systems allow the user to carry out these tasks via voice, touch, or other input methods.

Software

2009-09-16T01:32:00.000-07:00

Software, on the other hand, is the set of instructions a computer uses to manipulate data, such as a word-processing program or a video game. These programs are usually stored and transferred via the computer's hardware to and from the CPU. Software also governs how the hardware is utilized; for example, how information is retrieved from a storage device. The interaction between the input and output hardware is controlled by software called the Basic Input Output System software (BIOS).

Small Computer System Interface (SCSI)

2009-09-15T02:02:00.000-07:00

SCSI, acronym for small computer system interface, a standard high-speed parallel interface defined by the X3T9.2 committee of the American National Standards Institute (ANSI). A SCSI interface is used for connecting microcomputers to peripheral devices, such as hard disks and printers, and to other computers and local area networks.
Up to seven devices, not including the computer, can be attached through a single SCSI connection (port) through sequential connections called a daisy chain. Each device has an address (priority number). Only one device at a time can transmit through the port; priority is given to the device with the highest address. A SCSI port is standard on the Apple Macintosh Plus, Macintosh SE, Macintosh II, the IBM RS/6000, and the IBM PS/2 model 65 and higher computers. It can be installed in IBM PC and compatible computers as an expansion board.

Graphics Card

2009-09-15T01:59:00.000-07:00

Graphics Card, also called a video adapter, translates computer software instructions into images displayed on the monitor.

The graphics card is a printed circuit board that plugs into a slot in the main circuit board (motherboard) of the computer and determines horizontal scan rate (how fast the monitor's electron beam scans from top to bottom of the screen) and how many colors can be displayed; it must be compatible with the monitor.

Expansion Slots

2009-09-13T02:06:00.000-07:00

Expansion Slot, in computer science, a socket inside a computer console, designed to hold expansion boards and connect them to the system bus (data pathway). The number of sockets, or slots, determines the amount of expansion allowed. Most personal computers have from three to eight expansion slots. Expansion slots provide a means of adding new or enhanced features or more memory to the system.

Sound Card,

2009-09-13T02:04:00.000-07:00

Sound Card, printed circuit board, or card, that can translate digital information into sound and back; also called a sound board or sound adapter. Sound cards plug into a slot on the motherboard (the main circuit board of a computer) and are usually connected to a pair of speakers . To play sounds, the sound card receives digital information from a stored file and turns it into an electrical signal it sends to the speakers, which produce the sound.

If the sound card is attached to a microphone, the sound card can take the incoming sound and convert it into digital information by sampling, or taking tiny sections of, the sound many times each second (the most sophisticated sound cards can take almost 200,000 samples per second, but most take around 50,000 to 100,000 samples per second). Each sample is given a number that represents the loudness and tone of the sample and the order in which it occurs in the entire sound.

Expansion Boards

2009-09-12T02:05:00.000-07:00

Expansion Board, in computer science, circuit board holding chips and other electronic components connected by conductive paths that is plugged into a computer's bus (main data-transfer path) to add functions or resources to the computer. Typical expansion boards add memory, disk-drive controllers, video support, parallel and serial ports, and internal modems. The simple terms board and card are used interchangeably by most people to refer to all expansion boards.

MS - DOS Operating system

2009-09-05T01:58:00.003-07:00

MS-DOS, acronym for Microsoft Disk Operating System. In computer science, MS-DOS—like other operating systems—oversees such operations as disk input and output, video support, keyboard control, and many internal functions related to program execution and file maintenance. MS-DOS is a single-tasking, single-user operating system with a command-line interface.

MS - DOS Operating system

2009-09-05T01:58:00.002-07:00

Future Technologies in Operating Systems

2009-09-05T01:58:00.001-07:00

Operating systems continue to evolve. A recently developed type of OS called a distributed operating system is designed for a connected, but independent, collection of computers that share resources such as hard drives. In a distributed OS, a process can run on any computer in the network (presumably a computer that is idle) to increase that process's performance. All basic OS functions—such as maintaining file systems, ensuring reasonable behavior, and recovering data in the event of a partial failure—become more complex in distributed systems.

Research is also being conducted that would replace the keyboard with a means of using voice or handwriting for input. Currently these types of input are imprecise because people pronounce and write words very differently, making it difficult for a computer to recognize the same input from different users. However, advances in this field have led to systems that can recognize a small number of words spoken by a variety of people. In addition, software has been developed that can be taught to recognize an individual's handwriting.

Current Operating Systems

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Operating systems commonly found on personal computers include UNIX, Macintosh OS, and Windows. UNIX, developed in 1969 at AT&T Bell Laboratories, is a popular operating system among academic computer users. Its popularity is due in large part to the growth of the interconnected computer network known as the Internet. Software for the Internet was initially designed for computers that ran UNIX. Variations of UNIX include SunOS (distributed by SUN Microsystems, Inc.), Xenix (distributed by Microsoft Corporation), and Linux (available for download free of charge and distributed commercially by companies such as Red Hat, Inc.). UNIX and its clones support multitasking and multiple users. Its file system provides a simple means of organizing disk files and lets users control access to their files. The commands in UNIX are not readily apparent, however, and mastering the system is difficult. Consequently, although UNIX is popular for professionals, it is not the operating system of choice for the general public.

Instead, windowing systems with graphical interfaces, such as Windows and the Macintosh OS, which make computer technology more accessible, are widely used in personal computers (PCs). However, graphical systems generally have the disadvantage of requiring more hardware—such as faster CPUs, more memory, and higher-quality monitors—than do command-oriented operating systems.

Operating System 2 (O/S2)

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OS/2, or Operating System 2, operating system developed for the personal computer in the mid-1980s by International Business Machines Corporation (IBM) and Microsoft Corporation. An operating system is the set of software programs that controls the basic functions of a computer. The operating system coordinates and stores data entering and leaving the computer, controls the computer’s hardware (such as computer memory, keyboard, and mouse), and handles system errors.

At the time OS/2 was introduced in late 1987, the most common personal computers were IBM-compatible computers running the Microsoft Disk Operating System (MS-DOS) and computers manufactured by Apple Computer Corporation running Apple’s system for the Macintosh (Mac OS). The Macintosh operating system included multitasking, a feature that enabled computers to run several applications simultaneously. In a computer network, multitasking allows several users on different computers to have simultaneous access to the same application or data set. OS/2 was the first operating system designed for IBM-compatible personal computers that allowed multitasking.

The first version of OS/2, version 1.0, was text-oriented and lacked a graphical user interface (GUI) that would allow users to enter commands with a point-and-click input device, such as a computer mouse. A year later IBM and Microsoft released OS/2 version 1.1, which included a GUI called the Presentation Manager. The Presentation Manager interface contained icons, pictures or words on the screen that users could click on with a mouse to enter instructions. OS/2 version 1.1 also allowed users to have multiple windows open (windows are portions of the screen that each contain a different document or program) and included pull-down lists of commands that the user could choose by clicking on them with their mouse.

IBM and Microsoft ended their collaboration on OS/2 in 1991 after Microsoft released its Windows software, a multitasking environment that ran on MS-DOS. In 1992 IBM released version 2.0 of OS/2, which ran Microsoft Windows programs and could perform multitasking of DOS operations. It also contained an object-oriented programming environment that allowed software designers to create programs using high-level, object-oriented programming languages.

Subsequent versions of OS/2 offered enhanced performance and multimedia capabilities, and in 1994 IBM announced that more than 5 million copies of OS/2 had been sold since its introduction. The same year, IBM introduced a new version of OS/2 called OS/2 Warp that featured improved performance, more multimedia capabilities, an array of integrated applications, and easy access to the Internet. IBM has continued to upgrade and extend OS/2 Warp.

UNIX - Operating System

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UNIX, in computer science, a powerful multiuser, multitasking operating system. Considered a very powerful operating system, UNIX is written in the C language and can be installed on virtually any computer.

UNIX was originally developed by Ken Thompson and Dennis Ritchie at AT&T Bell Laboratories in 1969 for use on minicomputers. In the early 1970s, many universities, research institutions, and companies began to expand on and improve UNIX. These efforts resulted in two main versions: BSD UNIX, a version developed at the University of California at Berkeley, and System V, developed by AT&T and its collaborators.

Many companies developed and marketed their own versions of UNIX in subsequent years. Variations of UNIX include AIX, a version of UNIX adapted by IBM to run on RISC-based workstations; A/UX, a graphical version for the Apple Macintosh; XENIX OS, developed by Microsoft Corporation for 16-bit microprocessors; SunOS, adapted and distributed by Sun Microsystems, Inc.; Mach, a UNIX-compatible operating system for the NeXT computer; and Linux, developed by Finnish computer engineer Linus Torvalds with collaborators worldwide.

Windows - Operating System

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Windows, in computer science, personal computer operating system sold by Microsoft Corporation that allows users to enter commands with a point-and-click device, such as a mouse, instead of a keyboard. An operating system is a set of programs that control the basic functions of a computer. The Windows operating system provides users with a graphical user interface (GUI), which allows them to manipulate small pictures, called icons, on the computer screen to issue commands. Windows is the most widely used operating system in the world. It is an extension of and replacement for Microsoft’s Disk Operating System (MS-DOS).

The Windows GUI is designed to be a natural, or intuitive, work environment for the user. With Windows, the user can move a cursor around on the computer screen with a mouse. By pointing the cursor at icons and clicking buttons on the mouse, the user can issue commands to the computer to perform an action, such as starting a program, accessing a data file, or copying a data file. Other commands can be reached through pull-down or click-on menu items. The computer displays the active area in which the user is working as a window on the computer screen. The currently active window may overlap with other previously active windows that remain open on the screen. This type of GUI is said to include WIMP features: windows, icons, menus, and pointing device (such as a mouse).

Computer scientists at the Xerox Corporation’s Palo Alto Research Center (PARC) invented the GUI concept in the early 1970s, but this innovation was not an immediate commercial success. In 1983 Apple Computer featured a GUI in its Lisa computer. This GUI was updated and improved in its Macintosh computer, introduced in 1984.

Microsoft began its development of a GUI in 1983 as an extension of its MS-DOS operating system. Microsoft’s Windows version 1.0 first appeared in 1985. In this version, the windows were tiled, or presented next to each other rather than overlapping. Windows version 2.0, introduced in 1987, was designed to resemble IBM’s OS/2 Presentation Manager, another GUI operating system. Windows version 2.0 included the overlapping window feature. The more powerful version 3.0 of Windows, introduced in 1990, and subsequent versions 3.1 and 3.11 rapidly made Windows the market leader in operating systems for personal computers, in part because it was prepackaged on new personal computers. It also became the favored platform for software development.

In 1993 Microsoft introduced Windows NT (New Technology). The Windows NT operating system offers 32-bit multitasking, which gives a computer the ability to run several programs simultaneously, or in parallel, at high speed. This operating system competes with IBM’s OS/2 as a platform for the intensive, high-end, networked computing environments found in many businesses.

In 1995 Microsoft released a new version of Windows for personal computers called Windows 95. Windows 95 had a sleeker and simpler GUI than previous versions. It also offered 32-bit processing, efficient multitasking, network connections, and Internet access. Windows 98, released in 1998, improved upon Windows 95.

In 1996 Microsoft debuted Windows CE, a scaled-down version of the Microsoft Windows platform designed for use with handheld personal computers. Windows 2000, released at the end of 1999, combined Windows NT technology with the Windows 98 graphical user interface. In 2000 a special edition of Windows known as Windows Millenium Edition, or Windows ME, provided a more stable version of the Windows 98 interface. In 2001 Microsoft released a new operating system known as Windows XP, the company’s first operating system for consumers that was not based on MS-DOS.

Other popular operating systems include the Macintosh System (Mac OS) from Apple Inc., OS/2 Warp from IBM (see OS/2), and UNIX and its variations, such as Linux.

Working of an Operating System

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Operating systems control different computer processes, such as running a spreadsheet program or accessing information from the computer's memory. One important process is interpreting commands, enabling the user to communicate with the computer. Some command interpreters are text oriented, requiring commands to be typed in or to be selected via function keys on a keyboard. Other command interpreters use graphics and let the user communicate by pointing and clicking on an icon, an on-screen picture that represents a specific command. Beginners generally find graphically oriented interpreters easier to use, but many experienced computer users prefer text-oriented command interpreters.

Operating systems are either single-tasking or multitasking. The more primitive single-tasking operating systems can run only one process at a time. For instance, when the computer is printing a document, it cannot start another process or respond to new commands until the printing is completed.

All modern operating systems are multitasking and can run several processes simultaneously. In most computers, however, there is only one central processing unit (CPU; the computational and control unit of the computer), so a multitasking OS creates the illusion of several processes running simultaneously on the CPU. The most common mechanism used to create this illusion is time-slice multitasking, whereby each process is run individually for a fixed period of time. If the process is not completed within the allotted time, it is suspended and another process is run. This exchanging of processes is called context switching. The OS performs the “bookkeeping” that preserves a suspended process. It also has a mechanism, called a scheduler, that determines which process will be run next. The scheduler runs short processes quickly to minimize perceptible delay. The processes appear to run simultaneously because the user's sense of time is much slower than the processing speed of the computer.

Operating systems can use a technique known as virtual memory to run processes that require more main memory than is actually available. To implement this technique, space on the hard drive is used to mimic the extra memory needed. Accessing the hard drive is more time-consuming than accessing main memory, however, so performance of the computer slows.

Compiler

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Compiler, in computer science, computer program that translates source code, instructions in a program written by a software engineer, into object code, those same instructions written in a language the computer’s central processing unit (CPU) can read and interpret. Software engineers write source code using high level programming languages that people can understand. Computers cannot directly execute source code, but need a compiler to translate these instructions into a low level language called machine code.

Compilers collect and reorganize (compile) all the instructions in a given set of source code to produce object code. Object code is often the same as or similar to a computer’s machine code. If the object code is the same as the machine language, the computer can run the program immediately after the compiler produces its translation. If the object code is not in machine language, other programs—such as assemblers, binders, linkers, and loaders—finish the translation.

Most programming languages—such as C, C++, and Fortran—use compilers, but some—such as BASIC and LISP—use interpreters. An interpreter analyzes and executes each line of source code one-by-one. Interpreters produce initial results faster than compilers, but the source code must be re-interpreted with every use and interpreted languages are usually not as sophisticated as compiled languages.

Most computer languages use different versions of compilers for different types of computers or operating systems, so one language may have different compilers for personal computers (PC) and Apple Macintosh computers. Many different manufacturers often produce versions of the same programming language, so compilers for a language may vary between manufacturers.

Consumer software programs are compiled and translated into machine language before they are sold. Some manufacturers provide source code, but usually only programmers find the source code useful. Thus programs bought off the shelf can be executed, but usually their source code cannot be read or modified.

BASIC

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Hungarian-American mathematician John Kemeny and American mathematician Thomas Kurtz at Dartmouth College in Hanover, New Hampshire, developed BASIC (Beginner’s All-purpose Symbolic Instruction Code) in 1964. The language was easier to learn than its predecessors and became popular due to its friendly, interactive nature and its inclusion on early personal computers. Unlike languages that require all their instructions to be translated into machine code first, BASIC is turned into machine language line by line as the program runs. BASIC commands typify high-level languages because of their simplicity and their closeness to natural human language.

Assembly Level Languages

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Assembly language uses easy-to-remember commands that are more understandable to programmers than machine-language commands. Each machine language instruction has an equivalent command in assembly language. For example, in one Intel assembly language, the statement “MOV A, B” instructs the computer to copy data from location A to location B. The same instruction in machine code is a string of 16 0s and 1s. Once an assembly-language program is written, it is converted to a machine-language program by another program called an assembler.

Assembly language is fast and powerful because of its correspondence with machine language. It is still difficult to use, however, because assembly-language instructions are a series of abstract codes and each instruction carries out a relatively simple task. In addition, different CPUs use different machine languages and therefore require different programs and different assembly languages. Assembly language is sometimes inserted into a high-level language program to carry out specific hardware tasks or to speed up parts of the high-level program that are executed frequently.

Assembly Language, in computer science, a type of low-level computer programming language in which each statement corresponds directly to a single machine instruction. Assembly languages are thus specific to a given processor. After writing an assembly language program, the programmer must use the assembler specific to the microprocessor to translate the assembly language into machine code. Assembly language provides precise control of the computer, but assembly language programs written for one type of computer must be rewritten to operate on another type. Assembly language might be used instead of a high-level language for any of three major reasons: speed, control, and preference. Programs written in assembly language usually run faster than those generated by a compiler; use of assembly language lets a programmer interact directly with the hardware (processor, memory, display, and input/output ports).

High-Level Languages

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High-Level Language, in computer science, a computer language that provides a certain level of abstraction from the underlying machine language through the use of declarations, control statements, and other syntactical structures. In practice, the term comprises every computer language above assembly language.

Inheritance

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One especially powerful feature of OOP languages is a property known as inheritance. Inheritance allows an object to take on the characteristics and functions of other objects to which it is functionally connected. Programmers connect objects by grouping them together in different classes and by grouping the classes into hierarchies. These classes and hierarchies allow programmers to define the characteristics and functions of objects without needing to repeat source code, the coded instructions in a program. Thus, using OOP languages can greatly reduce the time it takes for a programmer to write an application, and also can reduce the size of the program. OOP languages are flexible and adaptable, so programs or parts of programs can be used for more than one task. Programs written with OOP languages are generally shorter in length and contain fewer bugs, or mistakes, than those written with non-OOP languages.

Machine Level Languages

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Low-Level Language, in computer science, a computerprogramming language that is machine-dependent and/or that offers few control instructions and data types. Each statement in a program written in a low-level language usually corresponds to one machine instruction. Assembly language is considered a low-level language.

Computer programs that can be run by a computer’s operating system are called executables. An executable program is a sequence of extremely simple instructions known as machine code. These instructions are specific to the individual computer’s CPU and associated hardware; for example, Intel Pentium and Power PC microprocessor chips each have different machine languages and require different sets of codes to perform the same task. Machine code instructions are few in number (roughly 20 to 200, depending on the computer and the CPU). Typical instructions are for copying data from a memory location or for adding the contents of two memory locations (usually registers in the CPU). Complex tasks require a sequence of these simple instructions. Machine code instructions are binary—that is, sequences of bits (0s and 1s). Because these sequences are long strings of 0s and 1s and are usually not easy to understand, computer instructions usually are not written in machine code. Instead, computer programmers write code in languages known as an assembly language or a high-level language.

Object Code

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Object Code, in computer science, translated version of source code—the statements of a particular computer program that can either be read by the computer directly, or read by the computer after it is further translated. Object code may also be called target code or the object program.

Object Oriented Programming

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Object-Oriented Programming (OOP), in computer science, type of high-level computer language that uses self-contained, modular instruction sets for defining and manipulating aspects of a computer program. These discrete, predefined instruction sets are called objects and they may be used to define variables, data structures, and procedures for executing data operations. In OOP, objects have built-in rules for communicating with one another. By using objects as stable, preexisting building blocks, programmers can pursue their main objectives and specify tasks from the top down, manipulating or combining objects to modify existing programs and to create entirely new ones.

Object-oriented programming began with Simula, a programming language developed from 1962 to 1967 by Ole-Johan Dahl and Kristen Nygaard at the Norwegian Computing Center in Oslo, Norway. Simula introduced definitive features of OOP, including objects and inheritance. In the early 1970s Alan Kay developed Smalltalk, another early OOP language, at the Palo Alto Research Center of the Xerox Corporation. Smalltalk made revolutionary use of a graphical user interface (GUI), a feature that allows the user to select commands using a mouse. GUIs became a central feature of operating systems such as Macintosh OS and Windows.

The most popular OOP language is C++, developed by Bjarne Stroustrup at Bell Laboratories in the early 1980s. In 1995 Sun Microsystems, Inc., released Java, an OOP language that can run on most types of computers regardless of platform. In some ways Java represents a simplified version of C++ but adds other features and capabilities as well, and it is particularly well suited for writing interactive applications to be used on the World Wide Web.

Object Oriented Programming Languages

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Object-oriented programming (OOP) languages, such as C++ and Java, are based on traditional high-level languages, but they enable a programmer to think in terms of collections of cooperating objects instead of lists of commands. Objects, such as a circle, have properties such as the radius of the circle and the command that draws it on the computer screen. Classes of objects can inherit features from other classes of objects. For example, a class defining squares can inherit features such as right angles from a class defining rectangles. This set of programming classes simplifies the programmer’s task, resulting in more “reusable” computer code. Reusable code allows a programmer to use code that has already been designed, written, and tested. This makes the programmer’s task easier, and it results in more reliable and efficient programs.

Other High Level Languages

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Other high-level languages in use today include C, C++, Ada, Pascal, LISP, Prolog, COBOL, Visual Basic, and Java. Some languages, such as the “markup languages” known as HTML, XML, and their variants, are intended to display data, graphics, and media selections, especially for users of the World Wide Web. Markup languages are often not considered programming languages, but they have become increasingly sophisticated.

Other High Level Languages

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Programming Languages

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Programming languages contain the series of commands that create software. A CPU has a limited set of instructions known as machine code that it is capable of understanding. The CPU can understand only this language. All other programming languages must be converted to machine code for them to be understood. Computer programmers, however, prefer to use other computer languages that use words or other commands because they are easier to use. These other languages are slower because the language must be translated first so that the computer can understand it. The translation can lead to code that may be less efficient to run than code written directly in the machine’s language.

Source Code

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Source Code, in computer science, human-readable program statements written in a high-level or assembly language, as opposed to object code, which is derived from the source code and designed to be machine-readable.

Vector Graphics

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Vector Graphics, in computer science, a method of generating images that uses mathematical descriptions to determine the position, length, and direction in which lines are to be drawn. In vector graphics, objects are created as collections of lines, rather than as patterns of individual dots (pixels), as is the case with raster graphics.

Raster Graphics

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Raster Graphics, in computer science, a method of generating graphics in which images are stored as multitudes of small, independently controlled dots (pixels) arranged in rows and columns. Raster graphics treats an image as a collection of such dots.

Post script font

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PostScript Font, in computer science, a font defined in terms of the PostScript page-description language rules and intended to be printed on a PostScript-compatible printer. PostScript fonts are distinguished from bit-mapped fonts by their smoothness, detail, and faithfulness to standards of quality established in the typographic industry. Fonts that appear on the screen—for example, as bit-mapped characters in a graphical user interface—are called screen fonts. When a document displayed in a screen font is sent to a PostScript printer, the printer uses the PostScript version if the font exists. If the font doesn't exist but a version is installed on the computer, that font is downloaded. If there is no PostScript font installed in either the printer or the computer, the bit-mapped font is translated into PostScript and the printer prints text using the bit-mapped font.

Pixel

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Pixel, in computer science, short for picture element; sometimes called a pel. One spot in a rectilinear grid of thousands of such spots that are individually “painted” to form an image produced on the screen by a computer or on paper by a printer. Just as a bit is the smallest unit of information a computer can process, a pixel is the smallest element that display or print hardware and software can manipulate in creating letters, numbers, or graphics.

An image can also be represented in more than two colors—for example, in a range of grays.

If a pixel has only two color values (typically black and white), it can be encoded by 1 bit of information. If more than 2 bits are used to represent a pixel, a larger range of colors or shades of gray can be represented: 2 bits for four colors or shades of gray, 4 bits for sixteen colors, and so on. Typically, an image of two colors is called a bit map, and an image of more than two colors is called a pixel map.

Object Oriented Graphics

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Object-Oriented Graphics, also called structured graphics. Computer graphics that are based on the use of “construction elements” (graphics primitives), such as lines, curves, circles, and squares. Object-oriented graphics, used in applications such as computer-aided design and drawing and illustration programs, describe an image mathematically as a set of instructions for creating the objects in the image. This approach contrasts with bit-mapped graphics, the other widely used approach to creating images, which represents a graphic as a group of black and white or colored dots arranged in a certain pattern. Object-oriented graphics enable the user to manipulate objects as entire units—for example, to change the length of a line or enlarge a circle—whereas bit-mapped graphics require repainting individual dots in the line or circle. Because objects are described mathematically, object-oriented graphics can also be layered, rotated, and magnified relatively easily.

Half tone imagery

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Halftone, the printed reproduction of a photograph or other illustration as a set of tiny, evenly spaced spots of variable diameter that, when printed, visually blur together to appear as shades of gray. Many printers used in desktop publishing, notably laser printers and digital imagesetters, are able to print halftone images. In traditional publishing, halftones are created by photographing an image through a meshlike screen; the darker the shade at a particular point in the image, the larger the spot in the resulting photograph. In desktop publishing, halftone spots are created electronically by mapping each gray level onto a collection of dots (called a spot) printed by the laser printer or imagesetter.

Font

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Font, traditionally, a set of characters of the same typeface (such as Courier), style (such as italic), stroke weight (such as bold), and size. A font is not to be confused with a typeface. Font refers to all the characters available in a particular size, style, and weight for a particular design; typeface refers to the design itself. Fonts are used by computers for on-screen displays and by printers for hard-copy output. In both cases, fonts are created either from bit maps (patterns of dots) or from outlines (as defined by a set of mathematical formulas). Programs that allow the use of different fonts are able to send information about typeface and size to a printer, even if they are not able to simulate different typefaces on the screen. The printer can then reproduce the font, provided either that the capability is built in or that a font description is available to the printer.

False Colour Imagey

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False-Color Imagery, graphic technique that displays images in false (not true-to-life) colors to enhance certain features. False-color imagery is widely used in displaying electronic images taken by spacecraft; for example, Earth-survey satellites such as Landsat. Any colors can be selected by a computer processing the data received from the satellite or spacecraft.

Clip Board

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Clipboard, in relation to computers, a special memory resource maintained by operating systems such as the Apple Macintosh operating system, Microsoft Windows, and the OS/2 Presentation Manager. A clipboard stores a copy of the last information that was “copied” or “cut.” A “paste” operation passes data from the clipboard to the current program. A clipboard allows information to be transferred from one program to another, provided the second program can read data generated by the first. Data copied using the clipboard is static and will not reflect later changes.

Clip Art

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Clip Art, in computer applications, such as desktop publishing and word-processing programs, collections of graphics that can be copied and added to brochures, newsletters, and other documents created with the programs. A wide variety of collections are available; some are packaged with programs, others can be purchased separately. Depending on the program, clip art images may be disassembled to allow a person to use only part of an image.

Bit Mapped Graphics

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Bit-Mapped Graphics, in computer science, computer graphics that are stored and held as collections of bits in memory locations corresponding to pixels on the screen. Bit-mapped graphics are typical of paint programs, which treat images as collections of dots rather than as shapes. Within a computer's memory, a bit-mapped graphic is represented as an array (group) of bits that describe the characteristics of the individual pixels making up the image. Bit-mapped graphics displayed in color require several to many bits per pixel, each describing some aspect of the color of a single spot on the screen.

Bit Image

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Bit Image, in computer science, a sequential collection of bits that represents, in memory, an image to be displayed on the screen, particularly in systems having a graphical user interface. Each bit in a bit image corresponds to one pixel (dot) on the screen. The screen itself, for example, represents a single bit image; similarly, the dot patterns for all the characters in a font represent a bit image of the font. On a computer such as the Macintosh 512K, which has a black-and-white screen, the bit values in a bit image can be either 0, to display white, or 1, to display black. The “pattern” of 0's and 1's in the bit image then determines the pattern of white and black dots forming an image on the screen. On a Macintosh or other computer that supports color, the corresponding description of on-screen bits is called a pixel image because more than one bit is needed to represent each pixel.

Graphical User Interface,

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Graphical User Interface (GUI), in computer science, a display format that enables the user to choose commands, start programs, and see lists of files and other options by pointing to pictorial representations (icons) and lists of menu items on the screen (see User Interface). Choices can generally be activated either with the keyboard or with a mouse. GUIs were inspired from the pioneering research of computer scientists at the Xerox Corporation's Palo Alto Research Center in the 1970s. Modern GUIs are used on the Macintosh operating system, Microsoft Windows, and the OS/2 Presentation Manager.

For application developers, GUIs offer an environment that processes the direct interaction with the computer. This frees the developer to concentrate on the application without worrying about the details of screen display, mouse control, or keyboard input. It also provides programmers standard controlling mechanisms for frequently repeated tasks such as opening windows and dialog boxes. Another benefit is that applications written for a GUI are device-independent: As the interface changes to support new input and output devices, such as a large-screen monitor or an optical storage device, the applications can, without modification, use those devices.

Firmware

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Although microprocessors are still technically considered to be hardware, portions of their function are also associated with computer software. Since microprocessors have both hardware and software aspects they are therefore often referred to as firmware

Firmware

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Byte

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Byte, a unit of information built from bits, the smallest units of information used in computers. Bits have one of two absolute values, either 0 or 1. These bit values physically correspond to whether transistors and other electronic circuitry in a computer are on or off. A byte is usually composed of 8 bits, although bytes composed of 16 bits are also used. See Number Systems.

The particular sequence of bits in the byte encodes a unit of information such as a keyboard character. One byte typically represents a single character such as a number, letter, or symbol. Most computers operate by manipulating groups of 2, 4, or 8 bytes called words.

Software designers use computers and software to combine bytes in complex ways and create meaningful data in the form of text files or binary files (files that contain data to be processed and interpreted by a computer). Bits and bytes are the basis for creating all meaningful information and programs on computers. For example, bits form bytes, which represent characters and can be combined to form words, sentences, paragraphs, and ultimately entire documents.

Bytes are the key unit for measuring quantity of data. Data quantity is commonly measured in kilobytes (1024 bytes), megabytes (1,048,576 bytes), or gigabytes (about 1 billion bytes). A regular, floppy disk normally holds 1.44 megabytes of data, which equates to approximately 1,400,000 keyboard characters, among other types of data. At this storage capacity, a single disk can hold a document approximately 700 pages long, with 2000 characters per page.

The term byte was first used in 1956 by Germanborn American computer scientist Werner Buchholz to prevent confusion with the word bit. He described a byte as a group of bits used to encode a character. The eight-bit byte was created that year and was soon adopted by the computer industry as a standard.

The number of bits used by a computer’s Central Processing Unit (CPU) for addressing information represents one measure of a computer’s speed and power. Computers today often use 16, 32, or 64 bits in groups of 2, 4, and 8 bytes in their addressing.

Byte

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Bit

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Bit, abbreviation for binary digit, the smallest unit of information in a computer. A bit is represented by the numbers 1 and 0, which correspond to the states on and off, true and false, or yes and no.

Bits are the building blocks for all information processing that goes on in digital electronics and computers. Bits actually represent the state of a transistor in the logic circuits of a computer. The number 1 (meaning on, yes, or true) is used to represent a transistor with current flowing through it—essentially a closed switch. The number 0 (meaning off, no, or false) is used to represent a transistor with no current flowing through it—an open switch. All computer information processing can be understood in terms of vast arrays of transistors (3.1 million transistors on the Pentium chip) switching on and off, depending on the bit value they have been assigned.

Bits are usually combined into larger units called bytes. A byte is composed of eight bits. The values that a byte can take on range between 00000000 (0 in decimal notation) and 11111111 (255 in decimal notation). This means that a byte can represent 28 (2 raised to the eighth power) or 256 possible states (0-255). Bytes are combined into groups of 1 to 8 bytes called words. The size of the words used by a computer’s central processing unit (CPU) depends on the bit-processing ability of the CPU. A 32-bit processor, for example, can use words that are up to four bytes long (32 bits).

Computers are often classified by the number of bits they can process at one time, as well as by the number of bits used to represent addresses in their main memory (RAM). Computer graphics are described by the number of bits used to represent pixels (short for picture elements), the smallest identifiable parts of an image. In monochrome images, each pixel is made up of one bit. In 256-color and gray-scale images, each pixel is made up of one byte (eight bits). In true color images, each pixel is made up of at least 24 bits.

The term bit was introduced by John Tukey, an American statistician and early computer scientist. He first used the term in 1946, as a shortened form of the term binary digit.

Hardware Connections

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To function, hardware requires physical connections that allow components to communicate and interact. A bus provides a common interconnected system composed of a group of wires or circuitry that coordinates and moves information between the internal parts of a computer. A computer bus consists of two channels, one that the CPU uses to locate data, called the address bus, and another to send the data to that address, called the data bus. A bus is characterized by two features: how much information it can manipulate at one time, called the bus width, and how quickly it can transfer these data.

A serial connection is a wire or set of wires used to transfer information from the CPU to an external device such as a mouse, keyboard, modem, scanner, and some types of printers. This type of connection transfers only one piece of data at a time, and is therefore slow. The advantage to using a serial connection is that it provides effective connections over long distances.

A parallel connection uses multiple sets of wires to transfer blocks of information simultaneously. Most scanners and printers use this type of connection. A parallel connection is much faster than a serial connection, but it is limited to distances of less than 3 m (10 ft) between the CPU and the external device.

Hardware Connections

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Hardware

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Hardware (computer), equipment involved in the function of a computer. Computer hardware consists of the components that can be physically handled. The function of these components is typically divided into three main categories: input, output, and storage. Components in these categories connect to microprocessors, specifically, the computer's central processing unit (CPU), the electronic circuitry that provides the computational ability and control of the computer, via wires or circuitry called a bus.

Education

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