ComputerVocabulary 9july2007

spam1
n. An unsolicited e-mail message sent to many recipients at one time, or a news article posted simultaneously to many newsgroups. Spam is the electronic equivalent of junk mail. In most cases, the content of a spam message or article is not relevant to the topic of the newsgroup or the interests of the recipient; spam is an abuse of the Internet in order to distribute a message (usually commercial or religious) to a huge number of people at minimal cost.
spam2
vb. To distribute unwanted, unrequested mail widely on the Internet by posting a message to too many recipients or too many newsgroups. The act of distributing such mail, known as spamming, angers most Internet users and has been known to invite retaliation, often in the form of return spamming that can flood and possibly disable the electronic
CPU cache
n. A section of fast memory linking the CPU (central processing unit) and main memory that temporarily stores data and instructions the CPU needs to execute upcoming commands and programs. Considerably faster than main memory, the CPU cache contains data that is transferred in blocks, thereby speeding execution. The system anticipates the data it will need through algorithms. Also called cache memory, memory cache. See also cache, CPU, VCACHE.
CPU
n. Acronym for central processing unit. The computational and control unit of a computer. The CPU is the device that interprets and executes instructions. Mainframes and early minicomputers contained circuit boards full of integrated circuits that implemented the CPU. Single-chip central processing units, called microprocessors, made possible personal computers and workstations. Examples of single-chip CPUs are the Motorola 68000, 68020, and 68030 chips and the Intel 8080, 8086, 80286, 80386, and i486 chips. The CPU-or microprocessor, in the case of a microcomputer-has the ability to fetch, decode, and execute instructions and to transfer information to and from other resources over the computer's main data-transfer path, the bus. By definition, the CPU is the chip that functions as the "brain" of a computer. In some instances, however, the term encompasses both the processor and the computer's memory or, even more broadly, the main computer console (as opposed to peripheral equipment). See also microprocessor.
microprocessor
n. A central processing unit (CPU) on a single chip. A modern microprocessor can have several million transistors in an integrated-circuit package that can easily fit into the palm of one's hand. Microprocessors are at the heart of all personal computers. When memory and power are added to a microprocessor, all the pieces, excluding peripherals, required for a computer are present. The most popular lines of microprocessors today are the 680x0 family from Motorola, which powers the Apple Macintosh line, and the 80x86 family from Intel, which is at the core of all IBM PC-compatible computers. See also 6502, 65816, 6800, 68000, 68020, 68030, 68040, 80286, 80386DX, 80386SX, 8080, 8086, 8088, 88000, DECchip 21064, i486DX, i486DX2, i486SL, i486SX, Pentium, PowerPC, SPARC, Z80.
programmable interrupt controller
n. An Intel chip that handles interrupt requests (IRQs). IBM AT machines use two programmable interrupt controllers to accommodate a maximum of 15 IRQs. The programmable interrupt controller has been replaced by the advanced programmable interrupt controller (APIC), which supports multiprocessing. Acronym: PIC. See also IBM AT, IRQ.
packet
n. 1. A unit of information transmitted as a whole from one device to another on a network. 2. In packet-switching networks, a transmission unit of fixed maximum size that consists of binary digits representing both data and a header containing an identification number, source and destination addresses, and sometimes error-control data. See also packet switching.
packet switching
n. A message-delivery technique in which small units of information (packets) are relayed through stations in a computer network along the best route available between the source and the destination. A packet-switching network handles information in small units, breaking long messages into multiple packets before routing. Although each packet may travel along a different path, and the packets composing a message may arrive at different times or out of sequence, the receiving computer reassembles the original message correctly. Packet-switching networks are considered to be fast and efficient. To manage the tasks of routing traffic and assembling/disassembling packets, such a network requires some intelligence from the computers and software that control delivery. The Internet is an example of a packet-switching network. Standards for packet switching on networks are documented in the -ITU recommendation X.25. Compare circuit switching.
circuit switching
n. A method of opening communications lines, as through the telephone system, by creating a physical link between the initiating and receiving parties. In circuit switching, the connection is made at a switching center, which physically connects the two parties and maintains an open line between them for as long as needed. Circuit switching is typically used on the dial-up telephone network, and it is also used on a smaller scale in privately maintained communications networks. Unlike other methods of transmission, such as packet switching, it requires the link to be established before any communication can take place. Compare message switching, packet switching
guru
n. A technical expert who is available to help solve problems and to answer questions in an intelligible way. See also techie, wizard (definition 1).

techie
n. A technically oriented person. Typically, a techie is the person on whom a user calls when something breaks or the user cannot understand a technical problem. A techie may be an engineer or a technician, but not all engineers are techies. See also guru
wizard
n. 1. Someone who is adept at making computers perform their "magic". A wizard is an outstanding and creative programmer or a power user. Compare guru, UNIX wizard. 2. A participant in a multiuser dungeon (MUD) who has permission to control the domain, even to delete other players' characters. See also MUD. 3. An interactive help utility within an application that guides the user through each step of a particular task, such as starting up a word processing document in the correct format for a business letter.
WYSBYGI
adj. Acronym for What You See Before You Get It. Providing a preview of the effects of the changes the user has selected before the changes are finally applied. For example, a dialog box in a word processing program might display a sample of the font a user has chosen before the font is actually changed in the document. The user can cancel any changes after previewing them, and the document will be unaffected. See also WYSIWYG.
WYSIWYG
adj. Acronym for What You See Is What You Get. Allowing a user to view a document as it will appear in the final product, and to directly edit the text, graphics, or other elements within that view. A WYSIWYG language is often easier to use than a markup language, which provides no immediate visual feedback regarding the changes being made. Compare markup language
markup language
n. A set of codes in a text file that instruct a computer how to format it on a printer or video display or how to index and link its contents. Examples of markup languages are Hypertext Markup Language (HTML) and Extensible Markup Language (XML), which are used in Web pages, and Standard Generalized Markup Language (SGML), which is used for typesetting and desktop publishing purposes and in electronic documents. Markup languages of this sort are designed to enable documents and other files to be platform-independent and highly portable between applications. See also HTML, SGML, XML.
interface
n. 1. The point at which a connection is made between two elements so that they can work with each other or exchange information. 2. Software that enables a program to work with the user (the user interface, which can be a command-line interface, menu-driven, or a graphical user interface), with another program such as the operating system, or with the computer's hardware. See also application programming interface, graphical user interface. 3. A card, plug, or other device that connects pieces of hardware with the computer so that information can be moved from place to place. For example, standardized interfaces such as RS-232-C standard and SCSI enable communications between computers and printers or disks. See also RS-232-C standard, SCSI.
proxy server
n. A firewall component that manages Internet traffic to and from a local area network (LAN) and can provide other features, such as document caching and access control. A proxy server can improve performance by supplying frequently requested data, such as a popular Web page, and can filter and discard requests that the owner does not consider appropriate, such as requests for unauthorized access to proprietary files. See also firewall.
proxy
n. A computer (or the software that runs on it) that acts as a barrier between a network and the Internet by presenting only a single network address to external sites. By acting as a go-between representing all internal computers, the proxy protects network identities while still providing access to the Internet. See also proxy server.
firewall
n. A security system intended to protect an organization's network against external threats, such as hackers, coming from another network, such as the Internet. Usually a combination of hardware and software, a firewall prevents computers in the organization's network from communicating directly with computers external to the network and vice versa. Instead, all communication is routed through a proxy server outside of the organization's network, and the proxy server decides whether it is safe to let a particular message or file pass through to the organization's network. See also proxy server.
.pdf
n. The file extension that identifies documents encoded in the Portable Document Format developed by Adobe Systems. In order to display or print a .pdf file, the user should obtain the freeware Adobe Acrobat Reader. See also Acrobat, Portable Document Format
Portable Document Format
n. The Adobe specification for electronic documents that use the Adobe Acrobat family of servers and readers. Acronym: PDF. See also Acrobat, .pdf.
portable language
n. A language that runs in the same way on different systems and therefore can be used for developing software for all of them. C, FORTRAN, and Ada are portable languages because their implementations on different systems are highly uniform; assembly language is extremely nonportable.
27octo05
Simple Mail Transfer Protocol
n. A TCP/IP protocol for sending messages from one computer to another on a network. This protocol is used on the Internet to route e-mail. Acronym: SMTP. See also communications protocol, TCP/IP. Compare CCITT X series, Post Office Protocol.
communications protocol
n. A set of rules or standards designed to enable computers to connect with one another and to exchange information with as little error as possible. The protocol generally accepted for standardizing overall computer communications is a seven-layer set of hardware and software guidelines known as the OSI (Open Systems Interconnection) model. A somewhat different standard, widely used before the OSI model was developed, is IBM's SNA (Systems Network Architecture). The word protocol is often used, sometimes confusingly, in reference to a multitude of standards affecting different aspects of communication, such as file transfer (for example, XMODEM and ZMODEM), handshaking (for example, XON/XOFF), and network transmissions (for example, CSMA/CD). See also ISO/OSI model, SNA.
snail mail
n. A popular phrase on the Internet for referring to mail services provided by the U.S. Postal Service and similar agencies in other countries. The term has its origins in the fact that regular postal mail is slow compared with e-mail.
24 MAY 2006
direct memory access29sep04
n. Memory access that does not involve the microprocessor and is frequently used for data transfer directly between memory and an intelligent peripheral device, such as a disk drive. Acronym: DMA.
n. An object-oriented version of the C programming language, developed by Bjarne Stroustrup in the early 1980s at Bell Laboratories and adopted by a number of vendors, including Apple Computer and Sun Microsystems, Inc. See also C, Objective-C, object-oriented programming.
ISV’s independent software vendors/8dec04
abstract data type/ 2dec04
n. In programming, a data set defined by the programmer in terms of the information it can contain and the operations that can be performed with it. An abstract data type is more generalized than a data type constrained by the properties of the objects it contains-for example, the data type "pet" is more generalized than the data types "pet dog," "pet bird," and "pet fish." The standard example used in illustrating an abstract data type is the stack", a small portion of memory used to store information, generally on a temporary basis. As an abstract data type, the stack is simply a structure onto which values can be pushed (added) and from which they can be popped (removed). The type of value, such as integer, is irrelevant to the definition.
The way in which the program performs operations on abstract data types is encapsulated, or hidden, from the rest of the program. Encapsulation enables the programmer to change the definition of the data type or its operations without introducing errors to the existing code that uses the abstract data type. Abstract data types represent an intermediate step between traditional programming and object-oriented programming. See also data type, object-oriented programming.
encapsulation
n. In object-oriented programming, the packaging of attributes (properties) and functionality (methods or behaviors) to create an object that is essentially a black box—one whose internal structure remains private and whose services can be accessed by other objects only through messages passed via a clearly defined interface (the programming equivalent of a mailbox or telephone line). Encapsulation ensures that the object providing service can prevent other objects from manipulating its data or procedures directly, and it enables the object requesting service to ignore the details of how that service is provided. See also information hiding.
fuzzy logic
n. A form of logic used in some expert systems and other artificial-intelligence applications in which variables can have degrees of truthfulness or falsehood represented by a range of values between 1 (true) and 0 (false). With fuzzy logic, the outcome of an operation can be expressed as a probability rather than as a certainty. For example, an outcome might be probably true, possibly true, possibly false, or probably false. See also expert system.
expert system/ 2dec04
n. An application program that makes decisions or solves problems in a particular field, such as finance or medicine, by using knowledge and analytical rules defined by experts in the field. It uses two components, a knowledge base and an inference engine, to form conclusions. Additional tools include user interfaces and explanation facilities, which enable the system to justify or explain its conclusions as well as allowing developers to run checks on the operating system. See also artificial intelligence, inference engine, intelligent database, encapsulation
n. In object-oriented programming, the packaging of attributes (properties) and functionality (methods or behaviors) to create an object that is essentially a black box—one whose internal structure remains private and whose services can be accessed by other objects only through messages passed via a clearly defined interface (the programming equivalent of a mailbox or telephone line). Encapsulation ensures that the object providing service can prevent other objects from manipulating its data or procedures directly, and it enables the object requesting service to ignore the details of how that service is provided. See also information hiding.
black box
n. A unit of hardware or software whose internal structure is unknown but whose function is documented. The internal mechanics of the function do not matter to a designer who uses a black box to obtain that function. For example, a memory chip can be viewed as a black box. Many people use memory chips and design them into computers, but generally only memory chip designers need to understand their internal operation.
encapsulate
vb. 1. To treat a collection of structured information as a whole without affecting or taking notice of its internal structure. In communications, a message or packet constructed according to one protocol, such as a TCP/IP packet, may be taken with its formatting data as an undifferentiated stream of bits that is then broken up and packaged according to a lower-level protocol (for example, as ATM packets) to be sent over a particular network; at the destination, the lower-level packets are assembled, re-creating the message as formatted for the encapsulated protocol. See also ATM (definition 1). 2. In object-oriented programming, to keep the implementation details of a class a separate file whose contents do not need to be known by a programmer using that class. See also object-oriented programming, TCP/IP.

information hiding
n. A design practice in which implementation details for both data structures and algorithms within a module or subroutine are hidden from routines using that module or subroutine, so as to ensure that those routines do not depend on some particular detail of the implementation. In theory, information hiding allows the module or subroutine to be changed without breaking the routines that use it. See also break, module, routine, subroutine.
module
n. 1. In programming, a collection of routines and data structures that performs a particular task or implements a particular abstract data type. Modules usually consist of two parts: an interface, which lists the constants, data types, variables, and routines that can be accessed by other modules or routines, and an implementation, which is private (accessible only to the module) and which contains the source code that actually implements the routines in the module. See also abstract data type, information hiding, Modula-2, modular programming. 2. In hardware, a self-contained component that can provide a complete function to a system and can be interchanged with other modules that provide similar functions. See also memory card, SIMM.
interface
n. 1. The point at which a connection is made between two elements so that they can work with each other or exchange information. 2. Software that enables a program to work with the user (the user interface, which can be a command-line interface, menu-driven, or a graphical user interface), with another program such as the operating system, or with the computer's hardware. See also application programming interface, graphical user interface. 3. A card, plug, or other device that connects pieces of hardware with the computer so that information can be moved from place to place. For example, standardized interfaces such as RS-232-C standard and SCSI enable communications between computers and printers or disks. See also RS-232-C standard, SCSI.
application programming interface
n. A set of routines used by an application program to direct the performance of procedures by the computer's operating system. Acronym: API. Also called application program interface.
graphical user interface/ 15dec04
n. A visual computer environment that represents programs, files, and options with graphical images, such as icons, menus, and dialog boxes on the screen. The user can select and activate these options by pointing and clicking with a mouse or, often, with the keyboard. A particular item (such as a scroll bar) works the same way to the user in all applications, because the graphical user interface provides standard software routines to handle these elements and report the user's actions (such as a mouse click on a particular icon or at a particular location in text, or a key press); applications call these routines with specific parameters rather than attempting to reproduce them from scratch. Acronym: GUI.
operating system
n. The software that controls the allocation and usage of hardware resources such as memory, central processing unit (CPU) time, disk space, and peripheral devices. The operating system is the foundation software on which applications depend. Popular operating systems include Windows 98, Windows NT, Mac OS, and UNIX. Acronym: OS. Also called executive.
virtual
adj. Of or pertaining to a device, service, or sensory input that is perceived to be what it is not in actuality, usually as more "real" or concrete than it actually is.
polymorphism
n. In an object-oriented programming language, the ability to redefine a routine in a derived class (a class that inherited its data structures and routines from another class). Polymorphism allows the programmer to define a base class that includes routines that perform standard operations on groups of related objects, without regard to the exact type of each object. The programmer then redefines the routines in the derived class for each type, taking into account the characteristics of the object. See also class, derived class, object (definition 2), object-oriented programming.
programmable interrupt controller
n. An Intel chip that handles interrupt requests (IRQs). IBM AT machines use two programmable interrupt controllers to accommodate a maximum of 15 IRQs. The programmable interrupt controller has been replaced by the advanced programmable interrupt controller (APIC), which supports multiprocessing. Acronym: PIC. See also IBM AT, IRQ
spam1
n. An unsolicited e-mail message sent to many recipients at one time, or a news article posted simultaneously to many newsgroups. Spam is the electronic equivalent of junk mail. In most cases, the content of a spam message or article is not relevant to the topic of the newsgroup or the interests of the recipient; spam is an abuse of the Internet in order to distribute a message (usually commercial or religious) to a huge number of people at minimal cost.
spam2
vb. To distribute unwanted, unrequested mail widely on the Internet by posting a message to too many recipients or too many newsgroups. The act of distributing such mail, known as spamming, angers most Internet users and has been known to invite retaliation, often in the form of return spamming that can flood and possibly disable the electronic mailbox of the original spammer.
31dec05
filter
n. 1. A program or set of features within a program that reads its standard or designated input, transforms the input in some desired way, and then writes the output to its standard or designated output destination. A database filter, for example, might flag information of a certain age. 2. In communications and electronics, hardware or software that selectively passes certain elements of a signal and eliminates or minimizes others. A filter on a communications network, for example, must be designed to transmit a certain frequency but attenuate (dampen) frequencies above it (a lowpass filter), those below it (a highpass filter), or those above and below it (a bandpass filter). 3. A pattern or mask through which data is passed to weed out specified items. For instance, a filter used in e-mail or in retrieving newsgroup messages can allow users to filter out messages from other users. See also e-mail filter, mask. 4. In computer graphics, a special effect or production effect that is applied to bitmapped images; for example, shifting pixels within an image, making elements of the image transparent, or distorting the image. Some filters are built into a graphics program, such as a paint program or an image editor. Others are separate software packages that plug into the graphics program. See also bitmapped graphics, image editor, paint program.
e-mail filter
n. A feature in e-mail-reading software that automatically sorts incoming mail into different folders or mailboxes based on information contained in the message. For example, all incoming mail from a user's Uncle Joe might be placed in a folder labeled "Uncle Joe". Filters may also be used either to block or accept e-mail from designated sources.
n. Short for picture (pix) element. 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. A pixel is the smallest element that display or print hardware and software can manipulate in creating letters, numbers, or graphics. Also called pel.
pixel image
n. The representation of a color graphic in a computer's memory. A pixel image is similar to a bit image, which also describes a screen graphic, but a pixel image has an added dimension, sometimes called depth, that describes the number of bits in memory assigned to each on-screen pixel.
pixel map
n. A data structure that describes the pixel image of a graphic, including such features as color, image, resolution, dimensions, storage format, and number of bits used to describe each pixel. See also pixel, pixel image.
31dec05
BIOS
n. Acronym for basic input/output system. On PC-compatible computers, the set of essential software routines that tests hardware at startup, starts the operating system, and supports the transfer of data among hardware devices. The BIOS is stored in read-only memory (ROM) so that it can be executed when the computer is turned on. Although critical to performance, the BIOS is usually invisible to computer users. See also AMI BIOS, CMOS setup, Phoenix BIOS, ROM BIOS. Compare Toolbox.
flip-flop
n. A circuit that alternates between two possible states when a pulse is received at the input. For example, if the output of a flip-flop is high and a pulse is received at the input, the output "flips" to low; a second input pulse "flops" the output back to high, and so on. Also called bistable multivibrator
float
n. The data type name used in some programming languages, notably C, to declare variables that can store floating-point numbers. See also data type, floating-point number, variable
floating-point number
n. A number represented by a mantissa and an exponent according to a given base. The mantissa is usually a value between 0 and 1. To find the value of a floating-point number, the base is raised to the power of the exponent, and the mantissa is multiplied by the result. Ordinary scientific notation uses floating-point numbers with 10 as the base. In a computer, the base for floating-point numbers is usually 2.
floating-point operation
n. An arithmetic operation performed on data stored in floating-point notation. Floating-point operations are used wherever numbers may have either fractional or irrational parts, as in spreadsheets and computer-aided design (CAD). Therefore, one measure of a computer's power is how many millions of floating-point operations per second (MFLOPS or megaflops) it can perform. Acronym: FLOP. Also called floating-point operation. See also floating-point notation, MFLOfloating-point notation
n. A numeric format that can be used to represent very large real numbers and very small real numbers. Floating-point numbers are stored in two parts, a mantissa and an exponent. The mantissa specifies the digits in the number, and the exponent specifies the magnitude of the number (the position of the decimal point). For example, the numbers 314,600,000 and 0.0000451 are expressed respectively as 3146E5 and 451E-7 in floating-point notation. Most microprocessors do not directly support floating-point arithmetic; consequently, floating-point calculations are performed either by using software or with a special floating-point processor. Also called exponential notation. See also fixed-point notation, floating-point processor, integer.
fixed-point notation
n. A numeric format in which the decimal point has a specified position. Fixed-point numbers are a compromise between integral formats, which are compact and efficient, and floating-point numeric formats, which have a great range of values. Like floating-point numbers, fixed-point numbers can have a fractional part, but operations on fixed-point numbers usually take less time than floating-point operations. See also floating-point notation, integer.
integer
n. 1. A positive or negative "whole" number, such as 37, -50, or 764. 2. A data type representing whole numbers. Calculations involving only integers are much faster than calculations involving floating-point numbers, so integers are widely used in programming for counting and numbering purposes. Integers can be signed (positive or negative) or unsigned (positive). They can also be described as long or short, depending on the number of bytes needed to store them. Short integers, stored in 2 bytes, cover a smaller range of numbers (for example, -32,768 through 32,767) than do long integers (for example, -2,147,483,648 through 2,147,483,647), which are stored in 4 bytes. Also called integral number. See also floating-point notation
byte
n. Short for binary term. A unit of data, today almost always consisting of 8 bits. A byte can represent a single character, such as a letter, a digit, or a punctuation mark. Because a byte represents only a small amount of information, amounts of computer memory and storage are usually given in kilobytes (1,024 bytes), megabytes (1,048,576 bytes), or gigabytes (1,073,741,824 bytes). Abbreviation: B. See also bit, gigabyte, kilobyte, megabyte. Compare octet, word.
character
n. A letter, number, punctuation mark, or other symbol or control code that is represented to a computer by one unit-1 byte-of information. A character is not necessarily visible, either on the screen or on paper; a space, for example, is as much a character as is the letter a or any of the digits 0 through 9. Because computers must manage not only so-called printable characters but also the look (formatting) and transfer of electronically stored information, a character can additionally indicate a carriage return or a paragraph mark in a word-processed document. It can be a signal to sound a beep, begin a new page, or mark the end of a file. See also ASCII, control character, EBCDIC.
nibble or nybble
n. Half a byte (4 bits). Compare quadbit.
ascii
n. In an FTP client program, the command that instructs the FTP server to send or receive files as ASCII text. See also ASCII, FTP client Compare binary2
ASCII
n. Acronym for American Standard Code for Information Interchange. A coding scheme using 7 or 8 bits that assigns numeric values to up to 256 characters, including letters, numerals, punctuation marks, control characters, and other symbols. ASCII was developed in 1968 to standardize data transmission among disparate hardware and software systems and is built into most minicomputers and all PCs. ASCII is divided into two sets: 128 characters (standard ASCII) and an additional 128 (extended ASCII). See also ASCII file, character, character code, control character, extended ASCII, standard ASCII. Compare EBCDIC.
EBCDIC.
ASCII character set
n. A standard 7-bit code for representing ASCII characters using binary values; code values range from 0 to 127. Most PC-based systems use an 8-bit extended ASCII code, with an extra 128 characters used to represent special symbols, foreign-language characters, and graphic symbols. See also ASCII, character, EBCDIC, extended ASCII, standard ASCII.
extended ASCII
n. Any set of characters assigned to ASCII values between decimal 128 and 255 (hexadecimal 80 through FF). The specific characters assigned to the extended ASCII codes vary between computers and between programs, fonts, or graphics characters. Extended ASCII adds capability by allowing for 128 additional characters, such as accented letters, graphics characters, and special symbols. See also ASCII.
C++
n. An object-oriented version of the C programming language, developed by Bjarne Stroustrup in the early 1980s at Bell Laboratories and adopted by a number of vendors, including Apple Computer and Sun Microsystems, Inc. See also C, Objective-C, object-oriented programming.
object-oriented programming
n. A programming paradigm in which a program is viewed as a collection of discrete objects that are self-contained collections of data structures and routines that interact with other objects. Acronym: OOP. See also C++, object (definition 2), Objective-C.
object-oriented programming
n. A programming paradigm in which a program is viewed as a collection of discrete objects that are self-contained collections of data structures and routines that interact with other objects. Acronym: OOP. See also C++, object (definition 2), Objective-C.
object
n. 1. Short for object code (machine-readable code). 2. In object-oriented programming, a variable comprising both routines and data that is treated as a discrete entity. See also abstract data type, module (definition 1), object-oriented programming. 3. In graphics, a distinct entity. For example, a bouncing ball might be an object in a graphics program.
module
n. 1. In programming, a collection of routines and data structures that performs a particular task or implements a particular abstract data type. Modules usually consist of two parts: an interface, which lists the constants, data types, variables, and routines that can be accessed by other modules or routines, and an implementation, which is private (accessible only to the module) and which contains the source code that actually implements the routines in the module. See also abstract data type, information hiding, Modula-2, modular programming. 2. In hardware, a self-contained component that can provide a complete function to a system and can be interchanged with other modules that provide similar functions. See also memory card, SIMM.
abstract data type
n. In programming, a data set defined by the programmer in terms of the information it can contain and the operations that can be performed with it. An abstract data type is more generalized than a data type constrained by the properties of the objects it contains-for example, the data type "pet" is more generalized than the data types "pet dog," "pet bird," and "pet fish." The standard example used in illustrating an abstract data type is the stack", a small portion of memory used to store information, generally on a temporary basis. As an abstract data type, the stack is simply a structure onto which values can be pushed (added) and from which they can be popped (removed). The type of value, such as integer, is irrelevant to the definition.
The way in which the program performs operations on abstract data types is encapsulated, or hidden, from the rest of the program. Encapsulation enables the programmer to change the definition of the data type or its operations without introducing errors to the existing code that uses the abstract data type. Abstract data types represent an intermediate step between traditional programming and object-oriented programming. See also data type, object-oriented programming.
data type
n. In programming, a definition of a set of data that specifies the possible range of values of the set, the operations that can be performed on the values, and the way in which the values are stored in memory. Defining the data type allows a computer to manipulate the data appropriately. Data types are most often supported in high-level languages and often include types such as real, integer, floating point, character, Boolean, and pointer. How a language handles data typing is one of its major characteristics. See also cast, constant, enumerated data type, strong typing, type checking, user-defined data type, variable, weak typing.
toolbox
n. A set of predefined (and usually precompiled) routines a programmer can use in writing a program for a particular machine, environment, or application. Also called toolkit. See also library (definition 1).
Toolbox
n. A set of routines stored mostly in the read-only memory of a Macintosh that provides application programmers with the tools needed to support the graphical interface characteristic of the computer. Also called User Interface Toolbox.

disk drive
n. An electromechanical device that reads from and writes to disks. The main components of a disk drive include a spindle on which the disk is mounted, a drive motor that spins the disk when the drive is in operation, one or more read/write heads, a second motor that positions the read/write head(s) over the disk, and controller circuitry that synchronizes read/write activities and transfers information to and from the computer. Two types of disk drives are in common use: floppy disk drives and hard disk drives. Floppy disk drives are designed to accept removable disks in either 5.25-inch or 3.5-inch format; hard disk drives are faster, high-capacity storage units that are completely enclosed in a protective case.
paradigm
n. An archetypal example or pattern that provides a model for a process or system
architecture
n. 1. The physical construction or design of a computer system and its components. See also cache, CISC, closed architecture, network architecture, open architecture, pipelining, RISC. 2. The data-handling capacity of a microprocessor. 3. The design of application software incorporating protocols and the means for expansion and interfacing with other programs.
cache
\kash\ n. A special memory subsystem in which frequently used data values are duplicated for quick access. A memory cache stores the contents of frequently accessed RAM locations and the addresses where these data items are stored. When the processor references an address in memory, the cache checks to see whether it holds that address. If it does hold the address, the data is returned to the processor; if it does not, a regular memory access occurs. A cache is useful when RAM accesses are slow compared with the microprocessor speed, because cache memory is always faster than main RAM memory. See also disk cache, wait state.
disk
n. 1. A round, flat piece of flexible plastic coated with a magnetic material that can be electrically influenced to hold information recorded in digital (binary) form and encased in a protective plastic jacket to protect them from damage and contamination. Also called floppy, floppy disk, microfloppy disk. Compare compact disc, disc. 2. See hard drive
compact disc
n. 1. An optical storage medium for digital data, usually audio. A compact disc is a nonmagnetic, polished metal disc with a protective plastic coating that can hold up to 74 minutes of high-fidelity recorded sound. The disk is read by an optical scanning mechanism that uses a high-intensity light source, such as a laser, and mirrors. Also called optical disc. 2. A technology that forms the basis of media such as CD-ROM, CD-ROM/XA, CD-I, CD-R, DVI, and PhotoCD. These media are all compact disc-based but store various types of digital information and have different read/write capabilities. Documentation for compact disc formats can be found in books designated by the color of their covers. For example, documentation for audio compact discs is found in the Red Book. See also CD-I, CD-R, CD-ROM, CD-ROM/XA, DVI, Green Book (definition 2), Orange Book (definition 2), PhotoCD, Red Book (definition 2). 3. See CD.
disc
n. A round, flat piece of nonmagnetic, shiny metal encased in a plastic coating, designed to be read from and written to by optical (laser) technology. It is now standard practice to use the spelling disc for optical discs and disk in all other computer contexts, such as floppy disk, hard disk, and RAM disk. See also compact disc.
RS-232-C standard
n. An accepted industry standard for serial communications connections. Adopted by the Electrical Industries Association, this Recommended Standard (RS) defines the specific lines and signal characteristics used by serial communications controllers to standardize the transmission of serial data between devices. The letter C denotes that the current version of the standard is the third in a series. See also CTS, DSR, DTR, RTS, RXD, TXD.
interactive processing
n. Processing that involves the more or less continuous participation of the user. Such a command/response mode is characteristic of microcomputers. Compare batch processing (definition 2).
interactive program
n. A program that exchanges output and input with the user, who typically views a display of some sort and uses an input device, such as a keyboard, mouse, or joystick, to provide responses to the program. A computer game is an interactive program. Compare batch program.
handshake
n. A series of signals acknowledging that communication or the transfer of information can take place between computers or other devices. A hardware handshake is an exchange of signals over specific wires (other than the data wires), in which each device indicates its readiness to send or receive data. A software handshake consists of signals transmitted over the same wires used to transfer data, as in modem-to-modem communications over telephone lines.
31dec05
communications protocol
n. A set of rules or standards designed to enable computers to connect with one another and to exchange information with as little error as possible. The protocol generally accepted for standardizing overall computer communications is a seven-layer set of hardware and software guidelines known as the OSI (Open Systems Interconnection) model. A somewhat different standard, widely used before the OSI model was developed, is IBM's SNA (Systems Network Architecture). The word protocol is often used, sometimes confusingly, in reference to a multitude of standards affecting different aspects of communication, such as file transfer (for example, XMODEM and ZMODEM), handshaking (for example, XON/XOFF), and network transmissions (for example, CSMA/CD). See also ISO/OSI model, SNA.
TCP/IP
n. Acronym for Transmission Control Protocol/Internet Protocol. A protocol suite (or set of protocols) developed by the Department of Defense for communications over interconnected, sometimes dissimilar, networks. It is built into the UNIX system and has become the de facto standard for data transmission over networks, including the Internet
1jan2006
spam1
n. An unsolicited e-mail message sent to many recipients at one time, or a news article posted simultaneously to many newsgroups. Spam is the electronic equivalent of junk mail. In most cases, the content of a spam message or article is not relevant to the topic of the newsgroup or the interests of the recipient; spam is an abuse of the Internet in order to distribute a message (usually commercial or religious) to a huge number of people at minimal cost.
spam2
vb. To distribute unwanted, unrequested mail widely on the Internet by posting a message to too many recipients or too many newsgroups. The act of distributing such mail, known as spamming, angers most Internet users and has been known to invite retaliation, often in the form of return spamming that can flood and possibly disable the electronic mailbox of the original spammer
6jan06
ADSL
n. Acronym for asymmetric digital subscriber line. Technology and equipment allowing high-speed digital communication, including video signals, across an ordinary twisted-pair copper phone line, with speeds up to 8 Mbps (megabits per second) downstream (to the customer) and up to 640 Kbps (kilobits per second) upstream. ADSL access to the Internet is offered by some regional telephone companies, offering users faster connection times than those available through connections made over standard phone lines. Also called asymmetric digital subscriber loop. Compare SDSL.
SDSL
n. Acronym for symmetric (or single-line) digital subscriber line, a digital telecommunications technology that is a variation of HDSL. SDSL uses one pair of copper wire rather than two pairs of wires and transmits at 1.544 Mbps. Compare ADSL.
VoIP
n. Acronym for Voice over IP. The use of the Internet Protocol (IP) for transmitting voice communications. VoIP delivers digitized audio in packet form and can be used for transmitting over intranets, extranets, and the Internet. It is essentially an inexpensive alternative to traditional telephone communication over the circuit-switched Public Switched Telephone Network (PSTN). VoIP covers computer-to-computer, computer-to-telephone, and telephone-based communications. For the sake of compatibility and interoperability, a group called the VoIP Forum promotes product development based on the ITU-T H.323 standard for transmission of multimedia over the Internet. Also called Internet telephony. See also H.323.
volatile memory
n. 1. Memory, such as RAM, that loses its data when the power is shut off. Compare nonvolatile memory. 2. Memory used by a program that can change independently of the program, such as memory shared by another program or by an interrupt service routine.
nonvolatile memory
n. A storage system that does not lose data when power is removed from it. Intended to refer to core memory, ROM, EPROM, flash memory, bubble memory, or battery-backed CMOS RAM, the term is occasionally used in reference to disk subsystems as well. See also bubble memory, CMOS RAM, core, EPROM, flash memory, ROM.
flash memory
n. A type of nonvolatile memory. Flash memory is similar to EEPROM memory in function but it must be erased in blocks, whereas EEPROM can be erased one byte at a time. Because of its block-oriented nature, flash memory is commonly used as a supplement to or replacement for hard disks in portable computers. In this context, flash memory either is built into the unit or, more commonly, is available as a PC Card that can be plugged into a PCMCIA slot. A disadvantage of the block-oriented nature of flash memory is that it cannot be practically used as main memory (RAM) because a computer needs to be able to write to memory in single-byte increments. See also EEPROM, nonvolatile memory, PC Card, PCMCIA slot
IP
n. Acronym for Internet Protocol. The protocol within TCP/IP that governs the breakup of data messages into packets, the routing of the packets from sender to destination network and station, and the reassembly of the packets into the original data messages at the destination. IP runs at the internetwork layer in the TCP/IP model-equivalent to the network layer in the ISO/OSI reference model. See also ISO/OSI reference model, TCP/IP. Compare TCP.
TCP
n. Acronym for Transmission Control Protocol. The protocol within TCP/IP that governs the breakup of data messages into packets to be sent via IP (Internet Protocol), and the reassembly and verification of the complete messages from packets received by IP. A connection-oriented, reliable protocol (reliable in the sense of ensuring error-free delivery), TCP corresponds to the transport layer in the ISO/OSI reference model. See also ISO/OSI reference model, packet, TCP/IP. Compare UDP.
packet
n. 1. A unit of information transmitted as a whole from one device to another on a network. 2. In packet-switching networks, a transmission unit of fixed maximum size that consists of binary digits representing both data and a header containing an identification number, source and destination addresses, and sometimes error-control data. See also packet switching.
USB
n. Acronym for universal serial bus. A serial bus with a data transfer rate of 12 megabits per second (Mbps) for connecting peripherals to a microcomputer. USB can connect up to 127 peripherals, such as external CD-ROM drives, printers, modems, mice, and keyboards, to the system through a single, general-purpose port. This is accomplished by daisy chaining peripherals together. USB is designed to support the ability to automatically add and configure new devices and the ability to add such devices without having to shut down and restart the system (hot plugging). USB was developed by Intel, Compaq, DEC, IBM, Microsoft, NEC, and Northern Telecom. It competes with DEC's ACCESS.bus for lower-speed applications. See also bus, daisy chain, hot plugging, input/output port, peripheral. Compare ACCESS.bus.
Micro Channel Architecture
n. The design of the bus in IBM PS/2 computers (except Models 25 and 30). The Micro Channel is electrically and physically incompatible with the IBM PC/AT bus. Unlike the PC/AT bus, the Micro Channel functions as either a 16-bit or a 32-bit bus. The Micro Channel also can be driven independently by multiple bus master processors.
PS/2 bus
n. See Micro Channel Architecture.
bus
n. A set of hardware lines (conductors) used for data transfer among the components of a computer system. A bus is essentially a shared highway that connects different parts of the system-including the processor, disk-drive controller, memory, and input/output ports-and enables them to transfer information. The bus consists of specialized groups of lines that carry different types of information. One group of lines carries data; another carries memory addresses (locations) where data items are to be found; yet another carries control signals. Buses are characterized by the number of bits they can transfer at a single time, equivalent to the number of wires within the bus. A computer with a 32-bit address bus and a 16-bit data bus, for example, can transfer 16 bits of data at a time from any of 232 memory locations. Most PCs contain one or more expansion slots into which additional boards can be plugged to connect them to the bus.
hard disk
n. A device containing one or more inflexible platters coated with material in which data can be recorded magnetically, together with their read/write heads, the head-positioning mechanism, and the spindle motor in a sealed case that protects against outside contaminants. The protected environment allows the head to fly 10 to 25 millionths of an inch above the surface of a platter rotating typically at 3,600 to 7,200 rpm; therefore, much more data can be stored and accessed much more quickly than on a floppy disk. Most hard disks contain from two to eight platters. Also called hard disk drive. Compare floppy disk.
soft copy
n. The temporary images presented on a computer display screen. Compare hard copy.
hard copy
n. Printed output on paper, film, or other permanent medium. Compare soft copy.
URL
n. Acronym for Uniform Resource Locator. An address for a resource on the Internet. URLs are used by Web browsers to locate Internet resources. A URL specifies the protocol to be used in accessing the resource (such as http: for a World Wide Web page or ftp: for an FTP site), the name of the server on which the resource resides (such as //www.whitehouse.gov), and, optionally, the path to a resource (such as an HTML document or a file on that server). See also FTP1 (definition 1), HTML, HTTP, path (definition 1), server (definition 2), virtual path (definition 1), Web browser.
HDSL
n. Acronym for High-bit-rate Digital Subscriber Line. A form of DSL, HDSL is a protocol for digital transmission of data over standard copper telecommunications lines (as opposed to fiber-optic lines) at rates of 1.544 Mbps in both directions. Also called High-data-rate Digital Subscriber Line. See also DSL.
broadband
adj. Of or relating to communications systems in which the medium of transmission (such as a wire or fiber-optic cable) carries multiple messages at a time, each message modulated on its own carrier frequency by means of modems. Broadband communication is found in wide area networks. Compare baseband.
8JAN06
optical communications
n. The use of light and of light-transmitting technology, such as optical fibers and lasers, in sending and receiving data, images, or sound.
n. A disk drive that reads and often can write data on optical (compact) discs. Examples of optical drives include CD-ROM drives and WORM disk drives. See also CD-ROM drive, compact disc, WORM.
optical fiber
n. A thin strand of transparent material used to carry optical signals. Optical fibers are constructed from special kinds of glass and plastic, and they are designed so that a beam of light introduced at one end will remain within the fiber, reflecting off the inner surfaces as it travels down the length of the fiber. Optical fibers are inexpensive, compact, and lightweight and are often packaged many hundred to a single cable. See also fiber optics.
optical mouse
n. A type of mouse that uses a pair of light-emitting diodes (LEDs) and a special reflective grid pad to detect motion. The two lights are of different colors, and the special mouse pad has a grid of lines in the same colors, one color for vertical lines and another for horizontal lines. Light detectors paired with the LEDs sense when a colored light passes over a line of the same color, indicating the direction of movement. See also mouse. Compare mechanical mouse, optomechanical mouse.
fiber optics
n. A technology for the transmission of light beams along optical fibers. A light beam, such as that produced in a laser, can be modulated to carry information. Because light has a higher frequency on the electromagnetic spectrum than other types of radiation, such as radio waves, a single fiber-optic channel can carry significantly more information than most other means of information transmission. Optical fibers are thin strands of glass or other transparent material, with dozens or hundreds of strands housed in a single cable. Optical fibers are essentially immune to electromagnetic interference. See also optical fiber.
mechanical mouse
n. A type of mouse in which the motion of a ball on the bottom of the mouse is translated into directional signals. As the user moves the mouse, the ball rolls, turning a pair of wheels mounted at right angles inside the mouse that have conductive markings on their surfaces. Because the markings permit an electric current to flow, a set of conductive brushes that ride on the surface of the conductive wheels can detect these conductive markings. The electronics in the mouse translate these electrical movement signals into mouse-movement information that can be used by the computer. See also mouse, trackball. Compare optical mouse, optomechanical mouse.
voice recognition
n. The capability of a computer to understand the spoken word for the purpose of receiving commands and data input from the speaker. Systems that can recognize limited vocabularies as spoken by specific individuals have been developed, but developing a system that deals with a variety of speech patterns and accents, as well as with the various ways in which a request or a statement can be made, is more difficult, although advances are being made in this area. Also called speech recognition. See also artificial intelligence, dictation software, neural network.
neural network
n. A type of artificial-intelligence system modeled after the neurons (nerve cells) in a biological nervous system and intended to simulate the way a brain processes information, learns, and remembers. A neural network is designed as an interconnected system of processing elements, each with a limited number of inputs and an output. These processing elements are able to "learn" by receiving weighted inputs that, with adjustment, time, and repetition, can be made to produce appropriate outputs. Neural networks are used in areas such as pattern recognition, speech analysis, and speech synthesis. See also artificial intelligence, pattern recognition (definition 1).
pattern recognition
n. 1. A broad technology describing the ability of a computer to identify patterns. The term usually refers to computer recognition of visual images or sound patterns that have been converted to arrays of numbers. 2. The recognition of purely mathematical or textual patterns.
thumbnail
n. A miniature version of an image or electronic version of a page that is generally used to allow quick browsing through multiple images or pages. For example, Web pages often contain thumbnails of images (which can be loaded much more quickly by the Web browser than the full-size image). Many of these thumbnails can be clicked on to load the complete version of the image
25jan06wednes
ADSL
n. Acronym for asymmetric digital subscriber line. Technology and equipment allowing high-speed digital communication, including video signals, across an ordinary twisted-pair copper phone line, with speeds up to 8 Mbps (megabits per second) downstream (to the customer) and up to 640 Kbps (kilobits per second) upstream. ADSL access to the Internet is offered by some regional telephone companies, offering users faster connection times than those available through connections made over standard phone lines. Also called asymmetric digital subscriber loop. Compare SDSL.
Post Office Protocol
n. A protocol for servers on the Internet that receive, store, and transmit e-mail and for clients on computers that connect to the servers to download and upload e-mail. Acronym: POP.
25jan06
digital signal processor
n. An integrated circuit designed for high-speed data manipulation and used in audio, communications, image manipulation, and other data acquisition and data control applications. Acronym: DSP
hardware
n. The physical components of a computer system, including any peripheral equipment such as printers, modems, and mouse devices. Compare firmware, software
26jan06

cookie
n. 1. A block of data that a server returns to a client in response to a request from the client. 2. On the World Wide Web, a block of data that a Web server stores on a client system. When a user returns to the same Web site, the browser sends a copy of the cookie back to the server. Cookies are used to identify users, to instruct the server to send a customized version of the requested Web page, to submit account information for the user, and for other administrative purposes. 3. Originally an allusion to fortune cookie, a UNIX program that outputs a different message, or "fortune", each time it is used. On some systems, the cookie program is run during user logon.
cache
\kash\ n. A special memory subsystem in which frequently used data values are duplicated for quick access. A memory cache stores the contents of frequently accessed RAM locations and the addresses where these data items are stored. When the processor references an address in memory, the cache checks to see whether it holds that address. If it does hold the address, the data is returned to the processor; if it does not, a regular memory access occurs. A cache is useful when RAM accesses are slow compared with the microprocessor speed, because cache memory is always faster than main RAM memory. See also disk cache, wait state.
benchmark1
n. A test used to measure hardware or software performance. Benchmarks for hardware use programs that test the capabilities of the equipment-for example, the speed at which a CPU can execute instructions or handle floating-point numbers. Benchmarks for software determine the efficiency, accuracy, or speed of a program in performing a particular task, such as recalculating data in a spreadsheet. The same data is used with each program tested, so the resulting scores can be compared to see which programs perform well and in what areas. The design of fair benchmarks is something of an art, because various combinations of hardware and software can exhibit widely variable performance under different conditions. Often, after a benchmark has become a standard, developers try to optimize a product to run that benchmark faster than similar products run it in order to enhance sales. See also sieve of Eratosthenes.
benchmark2
vb. To measure the performance of hardware or software.
benign virus
n. A program that exhibits properties of a virus, such as self-replication, but does not otherwise do harm to the computer systems that it infects.
2feb06
thumbnail
n. A miniature version of an image or electronic version of a page that is generally used to allow quick browsing through multiple images or pages. For example, Web pages often contain thumbnails of images (which can be loaded much more quickly by the Web browser than the full-size image). Many of these thumbnails can be clicked on to load the complete version of the image.
Java
n. An object-oriented programming language developed by Sun Microsystems. Similar to C++, Java is smaller, more portable, and easier to use than C++ because it is more robust and it manages memory on its own. Java was also designed to be secure and platform-neutral (meaning that it can be run on any platform) through the fact that Java programs are compiled into bytecode, which is not refined to the point of relying on platform-specific instructions and runs on a computer in a special software environment known as a virtual machine. This characteristic of Java makes it a useful language for programming Web applications, since users access the Web from many types of computers. Java is used in programming small applications, or applets, for the World Wide Web, as well as in creating distributed network applications. See also bytecode, Java applet, Jini, object-oriented programming.
platform
n. 1. The foundation technology of a computer system. Because computers are layered devices composed of a chip-level hardware layer, a firmware and operating-system layer, and an applications program layer, the bottommost layer of a machine is often called a platform. 2. In everyday usage, the type of computer or operating system being used.
transducer
n. A device that converts one form of energy into another. Electronic transducers either convert electric energy to another form of energy or convert nonelectric to electric energy.
IDE
n. Acronym for Integrated Device Electronics. A type of disk-drive interface in which the controller electronics reside on the drive itself, eliminating the need for a separate adapter card. The IDE interface is compatible with the controller used by IBM in the PC/AT computer but offers advantages such as look-ahead caching. See integrated development environment
integrated development environment
n. A set of integrated tools for developing software. The tools are generally run from one user interface and consist of a compiler, an editor, and a debugger, among others. Acronym: IDE.
multiplexer
n. A device for funneling several different streams of data over a common communications line. Multiplexers are used either to attach many communications lines to a smaller number of communications ports or to attach a large number of communications ports to a smaller number of communications lines. Acronym: MUX.
multiplexer channel
decoder
n. 1. A device or program routine that converts coded data back to its original form. This can mean changing unreadable or encrypted codes into readable text or changing one code to another, although the latter type of decoding is usually referred to as conversion. Compare conversion. 2. In electronics and hardware, a type of circuit that produces one or more selected output signals based on the combination of input signals it receives.
Wednesday, March 28, 2007

NotesMemory


flash memory
n. A type of nonvolatile memory. Flash memory is similar to EEPROM memory in function but it must be erased in blocks, whereas EEPROM can be erased one byte at a time. Because of its block-oriented nature, flash memory is commonly used as a supplement to or replacement for hard disks in portable computers. In this context, flash memory either is built into the unit or, more commonly, is available as a PC Card that can be plugged into a PCMCIA slot. A disadvantage of the block-oriented nature of flash memory is that it cannot be practically used as main memory (RAM) because a computer needs to be able to write to memory in single-byte increments. See also EEPROM, nonvolatile memory

nonvolatile memory
n. A storage system that does not lose data when power is removed from it. Intended to refer to core memory, ROM, EPROM, flash memory, bubble memory, or battery-backed CMOS RAM, the term is occasionally used in reference to disk subsystems as well. See also bubble memory, CMOS RAM, core, EPROM, flash memory 19Octo04

contiguous data structure/10nov04
n. A data structure, such as an array, that is stored in a consecutive set of memory locations. See also data structure. Compare noncontiguous data structure.
noncontiguous data structure/10nov04
n. In programming, a data structure whose elements are not stored contiguously in memory. Data structures such as graphs and trees, whose elements are connected by pointers, are noncontiguous data structures. Compare contiguous data structure.
Bit/10nov04
n. Short for binary digit. The smallest unit of information handled by a computer. One bit expresses a 1 or a 0 in a binary numeral, or a true or false logical condition, and is represented physically by an element such as a high or low voltage at one point in a circuit or a small spot on a disk magnetized one way or the other. A single bit conveys little information a human would consider meaningful. A group of 8 bits, however, makes up a byte, which can be used to represent many types of information, such as a letter of the alphabet, a decimal digit, or other character. See also ASCII, binary1, byte
byte/10nov04
n. Short for binary term. A unit of data, today almost always consisting of 8 bits. A byte can represent a single character, such as a letter, a digit, or a punctuation mark. Because a byte represents only a small amount of information, amounts of computer memory and storage are usually given in kilobytes (1,024 bytes), megabytes (1,048,576 bytes), or gigabytes (1,073,741,824 bytes). Abbreviation: B. See also bit, gigabyte, kilobyte, megabyte. Compare octet, word.

flash memory
n. A type of nonvolatile memory. Flash memory is similar to EEPROM memory in function but it must be erased in blocks, whereas EEPROM can be erased one byte at a time. Because of its block-oriented nature, flash memory is commonly used as a supplement to or replacement for hard disks in portable computers. In this context, flash memory either is built into the unit or, more commonly,

is available as a PC Card that can be plugged into a PCMCIA slot. A disadvantage of the block-oriented nature of flash memory is that it cannot be practically used as main memory (RAM) because a computer needs to be able to write to memory in single-byte increments. See also EEPROM, nonvolatile memory, PC Card, PCMCIA slot.

kernel
n. The core of an operating system-the portion of the system that manages memory, files, and peripheral devices; maintains the time and date; launches applications; and allocates system resources.
Wednesday, May 02, 2007
Linux
n. A version of the UNIX System V Release 3.0 kernel developed for PCs with 80386 and higher-level microprocessors. Developed by Linus Torvalds (for whom it is named) along with numerous collaborators worldwide, Linux is distributed free, and its source code is open to modification by anyone who chooses to work on it, although some companies distribute it as part of a commercial package with Linux-compatible utilities. The Linux kernel works with the GNU utilities developed by the Free Software Foundation, which did not produce a kernel. It is used by some as an operating system for network servers and in the 1998/1999 timeframe began to gain increased visibility through support from vendors such as IBM and Compaq. See also free software, GNU, kernel, UNIX.
UNIX
n. A multiuser, multitasking operating system. Originally developed by Ken Thompson and Dennis Ritchie at AT&T Bell Laboratories from 1969 through 1973 for use on minicomputers, UNIX has evolved into a complex, powerful operating system that, because it is written in the C language, is more portable-that is, less machine-specific-than many other operating systems. UNIX has been released in a wide variety of versions, or flavors, including System V (developed by AT&T for commercial release; many current flavors on based on it), BSD UNIX (freeware developed at the University of California Berkeley, which has spun off many related flavors) AIX (a version of System V adapted by IBM to run on RISC-based workstations), A/UX (a graphical version for the Macintosh), Linux (a newer version that runs on the Intel chip), and SunOS (based on BSD UNIX and available on Sun workstations). Many flavors of UNIX are available free. With some flavors, the source code is also free, making it an instrumental part of the Open Source movement. UNIX is a widely used as a network operating system, especially in conjunction with the Internet. See also BSD UNIX, Linux, open source, System V.
open source
n. The practice of making the source code (program instructions) for a software product freely available, at no cost, to interested users and developers, even though they were not involved in creating the original product. The distributors of open source software expect and encourage users and outside programmers to examine the code in order to identify problems, and to modify the code with suggested improvements and enhancements. Widely used open-source products include the Linux operating system and the Apache web server.
open system
n. 1. In communications, a computer network designed to incorporate all devices-regardless of the manufacturer or model-that can use the same communications facilities and protocols. 2. In reference to computer hardware or software, a system that can accept add-ons produced by third-party suppliers. See also open architecture (definition 1).
open architecture
n. 1. Any computer or peripheral design that has published specifications. A published specification lets third parties develop add-on hardware for a computer or device. Compare closed architecture (definition 1). 2. A design that provides for expansion slots on the motherboard, thereby allowing the addition of boards to enhance or customize a system. Compare closed architecture (definition 2).
closed architecture
n. 1. Any computer design whose specifications are not freely available. Such proprietary specifications make it difficult or impossible for third-party vendors to create ancillary devices that work correctly with a closed-architecture machine; usually only its original maker can build peripherals and add-ons for such a machine. Compare open architecture (definition 1). 2. A computer system that provides no expansion slots for adding new types of circuit boards within the system unit. The original Apple Macintosh was an example of a closed architecture. Compare open architecture (definition 2).
operating system
n. The software that controls the allocation and usage of hardware resources such as memory, central processing unit (CPU) time, disk space, and peripheral devices. The operating system is the foundation software on which applications depend. Popular operating systems include Windows 98, Windows NT, Mac OS, and UNIX. Acronym: OS. Also called executive.
RAM
n. Acronym for random access memory. Semiconductor-based memory that can be read and written by the central processing unit (CPU) or other hardware devices. The storage locations can be accessed in any order. Note that the various types of ROM memory are capable of random access but cannot be written to. The term RAM, however, is generally understood to refer to volatile memory that can be written to as well as read. Compare core, EPROM, flash memory, PROM, ROM (definition 2).
ROM
n. 1. Acronym for read-only memory. A semiconductor circuit into which code or data is permanently installed by the manufacturing process. The use of this technology is economically viable only if the chips are produced in large quantities; experimental designs or small volumes are best handled using PROM or EPROM. 2. Acronym for read-only memory. Any semiconductor circuit serving as a memory that contains instructions or data that can be read but not modified (whether placed there by manufacturing or by a programming process, as in PROM and EPROM). See also EEPROM, EPROM, PROM
volatile memory
n. 1. Memory, such as RAM, that loses its data when the power is shut off. Compare nonvolatile memory. 2. Memory used by a program that can change independently of the program, such as memory shared by another program or by an interrupt service routine.
nonvolatile memory
n. A storage system that does not lose data when power is removed from it. Intended to refer to core memory, ROM, EPROM, flash memory, bubble memory, or battery-backed CMOS RAM, the term is occasionally used in reference to disk subsystems as well. See also bubble memory, CMOS RAM, core, EPROM, flash memory, ROM.
flash memory
n. A type of nonvolatile memory. Flash memory is similar to EEPROM memory in function but it must be erased in blocks, whereas EEPROM can be erased one byte at a time. Because of its block-oriented nature, flash memory is commonly used as a supplement to or replacement for hard disks in portable computers. In this context, flash memory either is built into the unit or, more commonly, is available as a PC Card that can be plugged into a PCMCIA slot. A disadvantage of the block-oriented nature of flash memory is that it cannot be practically used as main memory (RAM) because a computer needs to be able to write to memory in single-byte increments. See also EEPROM, nonvolatile memory, PC Card, PCMCIA slot.
hacker
n. 1. A computerphile; a person who is totally engrossed in computer technology and computer programming or who likes to examine the code of operating systems and other programs to see how they work. 2. A person, more commonly considered a cracker, who uses computer expertise for illicit ends, such as by gaining access to computer systems without permission and tampering with programs and data. Also called cracker.

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