-= webopćdia, ver 1.1 =-

Bus
/bus/

A collection of wires through which data is transmitted from one part of a computer to another. You can think of a bus as a highway on which data travels within a computer. When used in reference to personal computers, the term bus usually refers to internal bus. This is a bus that connects all the internal computer components to the CPU and main memory. There's also an expansion bus that enables expansion boards to access the CPU and memory. All buses consist of two parts -- an address bus and a data bus. The data bus transfers actual data whereas the address bus transfers information about where the data should go. The size of a bus, known as its width, is important because it determines how much data can be transmitted at one time. For example, a 16-bit bus can transmit 16 bits of data, whereas a 32-bit bus can transmit 32 bits of data. Every bus has a clock speed measured in MHz. A fast bus allows data to be transferred faster, which makes applications run faster. On PCs, the old isa bus is being replaced by faster buses such as PCI. Nearly all PCs made today include a local bus for data that requires especially fast transfer speeds, such as video data. The local bus is a high-speed pathway that connects directly to the processor. Several different types of buses are used on Apple Macintosh computers. Older Macs use a bus called Nubus, but newer ones use PCI.

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C

C++
/sE plus plus/

A high-level programming language developed by Bjarne Stroustrup at Bell Labs. C++ adds object-oriented features to its predecessor, C. C++ is one of the most popular programming language for graphical applications, such as those that run in Windows and Macintosh environments.

Cache
/kash/

Pronounced cash, a special high-speed storage mechanism. It can be either a reserved section of main memory or an independent high-speed storage device. Two types of caching are commonly used in personal computers: memory caching and disk caching. A memory cache, sometimes called a cache store or RAM cache, is a portion of memory made of high-speed static RAM (SRAM) instead of the slower and cheaper dynamic RAM (DRAM) used for main memory. Memory caching is effective because most programs access the same data or instructions over and over. By keeping as much of this information as possible in SRAM, the computer avoids accessing the slower DRAM. Some memory caches are built into the architecture of microprocessors. The Intel 80/486 microprocessor, for example, contains an 8K memory cache, and the Pentium has a 16K cache. Such internal caches are often called Level 1 (L1) caches. Most modern PCs also come with external cache memory, called Level 2 (L2) caches. These caches sit between the CPU and the DRAM. Like L1 caches, L2 caches are composed of SRAM but they are much larger. Disk caching works under the same principle as memory caching, but instead of using high-speed SRAM, a disk cache uses conventional main memory. The most recently accessed data from the disk (as well as adjacent sectors) is stored in a memory buffer. When a program needs to access data from the disk, it first checks the disk cache to see if the data is there. Disk caching can dramatically improve the performance of applications, because accessing a byte of data in RAM can be thousands of times faster than accessing a byte on a hard disk. When data is found in the cache, it is called a cache hit, and the effectiveness of a cache is judged by its hit rate. Many cache systems use a technique known as smart caching, in which the system can recognize certain types of frequently used data. The strategies for determining which information should be kept in the cache constitute some of the more interesting problems in computer science.

CGI - Common Gateway Interface
/sE jE I/ or /kom-mun gAt-wa in-ter-fass/

CGI is a specification for transferring information between a World Wide Web server and a CGI program. A CGI program is any program designed to accept and return data that conforms to the CGI specification. The program could be written in any programming language, including C, perl, Java, or Visual Basic. CGI programs are the most common way for Web servers to interact dynamically with users. Many HTML pages that contain forms, for example, use a CGI program to process the form's data once it's submitted. Another increasingly common way to provide dynamic feedback for Web users is to include scripts or programs that run on the user's machine rather than the Web server. These programs can be Java applets, Java scripts, or ActiveX controls. These technologies are known collectively as client-side solutions, while the use of CGI is a server-side solution because the processing occurs on the Web server. One problem with CGI is that each time a CGI script is executed, a new process is started. For busy Web sites, this can slow down the server noticeably. A more efficient solution, but one that it is also more difficult to implement, is to use the server's API, such as ISAPI or NSAPI. Another increasingly popular solution is to use Java servlets.

CHAP - Challenged Handshake Authentication Protocol
/chap/

CHAP is a type of authentication in which the authentication agent (typically a network server) sends the client program a key to be used to encrypt the username and password. This enables the username and password to be transmitted in an encrypted form to protect them against eavesdroppers. Contrasts with PAP.

Client
/klI-ent/

The client part of a client-server architecture. Typically, a client is an application that runs on a personal computer or workstation and relies on a server to perform some operations. For example, an e-mail client is an application that enables you to send and receive e-mail.

Client\Server Architecture
/klI-ent sir-vir ark-i-tek-chir/

A network architecture in which each computer or process on the network is either a client or a server. Servers are powerful computers or processes dedicated to managing disk drives (file servers), printers (print servers), or network traffic (network servers). Clients are PCs or workstations on which users run applications. Clients rely on servers for resources, such as files, devices, and even processing power. Another type of network architecture is known as a peer-to-peer architecture because each node has equivalent responsibilities. Both client/server and peer-to-peer architectures are widely used, and each has unique advantages and disadvantages. Client-server architectures are sometimes called two-tier architectures.

Cookie
/kew-kE/

A message given to a Web browser by a Web server. The browser stores the message in a text file called cookie.txt. The message is then sent back to the server each time the browser requests a page from the server. The main purpose of cookies is to identify users and possibly prepare customized Web pages for them. When you enter a Web site using cookies, you may be asked to fill out a form providing such information as your name and interests. This information is packaged into a cookie and sent to your Web browser which stores it for later use. The next time you go to the same Web site, your browser will send the cookie to the Web server. The server can use this information to present you with custom Web Pages. So, for example, instead of seeing just a generic welcome page you might see a welcome page with your name on it. The name cookie derives from Unix objects called magic cookies. These are tokens that are attached to a user or program and change depending on the areas entered by the user or program. Cookies are also sometimes called persistent cookies because they typically stay in the browser for long periods of time.

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D

DHCP - Dynamic Host Configuration Protocol
/dE Ach sE pE/ or /dI-nam-ik hOst prO-tO-kol/

DHCP is a protocol for assigning dynamic IP addresses to devices on a network. With dynamic addressing, a device can have a different IP address every time it connects to the network. In some systems, the device's IP address can even change while it is still connected. DHCP also supports a mix of static and dynamic IP addresses. Dynamic addressing simplifies network administration because the software keeps track of IP addresses rather than requiring an administrator to manage the task. This means that a new computer can be added to a network without the hassle of manually assigning it a unique IP address. Many ISPs use dynamic IP addressing for dial-up users. DHCP client support is built into Windows 95 and NT workstation. NT 4 server includes both client and server support.

Digital Signature
/dij-i-tul sig-nuh-chir/

A digital code that can be attached to an electronically transmitted message that uniquely identifies the sender. Like a written signature, the purpose of a digital signature is to guarantee that the individual sending the message really is who he or she claims to be. Digital signatures are especially important for electronic commerce and are a key component of most authentication schemes. To be effective, digital signatures must be unforgeable. There are a number of different encryption techniques to guarantee this level of security.

Domain
/dO-mAn/

A group of computers and devices on a network that are administered as a unit with common rules and procedures. Within the Internet, domains are defined by the IP address. All devices sharing a common part of the IP address are said to be in the same domain.

DLL - Dynamic Link Library
/dE el el/ or /dI-nam-ik lEnk lI-brar-E/

A DLL is a library of executable functions or data that can be used by a Windows application. Typically, a DLL provides one or more particular functions and a program accesses the functions by creating either a static or dynamic link to the DLL. A static link remains constant during program execution while a dynamic link is created by the program as needed. DLLs can also contain just data. DLL files usually end with the extension .dll,.exe., drv, or .fon. A DLL can be used by several applications at the same time. Some DLLs are provided with the Windows operating system and available for any Windows application. Other DLLs are written for a particular application and are loaded with the application.

DMA - Dynamic Memory Address
/dE em A/ or /dI-nam-ik mem-or-E ad-jres/

A DMA is a technique for transferring data from main memory to a device without passing it through the CPU. Computers that have DMA channels can transfer data to and from devices much more quickly than computers without a DMA channel can. This is useful for making quick backups and for real-time applications. Some expansion boards, such as CD-ROM cards, are capable of accessing the computer's DMA channel. When you install the board, you must specify which DMA channel is to be used, which sometimes involves setting a jumper or DIP switch.

DNS - Domain Name Service
/dE en es/ or /dOh-mAn nAm sir-ves/

A DNS is an Internet service that translates domain names into IP addresses. Because domain names are alphabetic, they're easier to remember. The Internet however, is really based on IP addresses. Every time you use a domain name, therefore, a DNS service must translate the name into the corresponding IP address. For example, the domain name www.example.com might translate to 198.105.232.4. The DNS system is, in fact, its own network. If one DNS server doesn't know how to translate a particular domain name, it asks another one, and so on, until the correct IP address is returned.

DRAM - Dynamic Random Access Memory
/jram/ or /dI-nam-ik ran-dum ak-ses mem-or-E/

DRAM is a type of memory used in most personal computers.

DUN - Dial-Up Networking
/dun/ or /dI-al up net-werk-Eng/

A component in Windows 95 that enables you to connect your computer to a network via a modem. If your computer is not connected to a LAN and you want to connect to the Internet, you need to configure Dial-Up Networking (DUN) to dial a Point of Presence (POP) and log into your Internet Service Provider (ISP). Your ISP will need to provide certain information, such as the gateway address and your computer's IP address. You access DUN through the My Computer icon. You can configure a different profile (called a connectoid) for each different online service you use. Once configured, you can copy a connectoid shortcut to your desktop so that all you need to do to make a connection is double-click the connectoid icon.

DVD - Digital Versatile Disk or Digital Video Disk
/dE vE dE/ or /dij-i-tul vir-suh-tuhl disk or dij-i-tul vi-dE-Oh disk/

DVD is a new type of CD-ROM that holds a minimum of 4.7GB (gigabytes). Many experts believe that DVD disks, called DVD-ROMs, will eventually replace CD-ROMs, as well as VHS video cassettes and laser discs. The DVD specification supports disks with capacities from 4.7GB to 17GB and access rates of 600 kbps to 1.3 MBps. One of the best features of DVD drives is that they are backward-compatible with CD-ROMs. This means that DVD players can play old CD-ROMs, CD-I disks, and video CDs, as well as new DVD-ROMs. Newer DVD players, called second-generation or DVD-2 drives, can also read CD-R and CD-RW disks. The 4.7 gig capacity of a DVD disk is not enough to contain a full-length movie, and therefore they use a compression standard called mpeg-2.

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E

EDO DRAM - Extended Data Output Dynamic Random Access Memory
/E dE Oh jram/ or /ex-ten-ded dAtuh owt-put dI-nam-ik ran-dum ak-ses mem-or-E/

This is a type of DRAM that is faster than conventional DRAM. Unlike conventional DRAM which can only access one block of data at a time, EDO RAM can start fetching the next block of memory at the same time that it sends the previous block to the CPU.

EIDE - Enhanced Intelligent Drive Electronics or Integrated Drive Electronics
/E I dE E/ or /en-han-sd in-tel-i-jent jrIv el-ek-chron-iks or in-te-grA-ted jrIv el-ek-chron-iks/

A newer version of the IDE mass storage device interface standard developed by Western Digital Corporation. It supports data rates of between 4 and 16.6 MBps, about three to four times faster than the old IDE standard. In addition, it can support mass storage devices of up to 8.4 gigabytes, whereas the old standard was limited to 528 MB. Because of its lower cost, enhanced EIDE has replaced SCSI in many areas. EIDE is sometimes referred to as Fast ATA or Fast IDE, which is essentially the same standard, developed and promoted by Seagate Technologies. It is also sometimes called ATA-2. There are four EIDE modes defined. The most common is Mode 4, which supports transfer rates of 16.6 MBps. There is also a new mode, called ATA-3 or Ultra ATA, that supports transfer rates of 33 MBps.

Ethernet
/E-ther-net/

A local-area network (LAN) protocol developed by Xerox Corporation in cooperation with DEC and Intel in 1976. Ethernet uses a bus or star topology and supports data transfer rates of 10 Mbps. The Ethernet specification served as the basis for the IEEE 802.3 standard, which specifies the physical and lower software layers. Ethernet uses the CSMA/CD access method to handle simultaneous demands. It is one of the most widely implemented LAN standards. A newer version of Ethernet, called 100Base-T (or Fast Ethernet), supports data transfer rates of 100 Mbps. And the newest version, Gigabit Ethernet supports data rates of 1 gigabit (1,000 megabits) per second.

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F

FAT - File Alocation Table
/fat/ or /fI-el al-O-kA-shun tA-bel/

A table that the operating system uses to locate files on a disk. Due to fragmentation, a file may be divided into many sections that are scattered around the disk. The FAT keeps track of all these pieces.

In DOS systems, FATs are stored in hidden files, called FAT files .

The FAT system for older versions of Windows 95 is called VFAT, and the one for new versions of Windows 95 and Windows 98 is called either FAT16 or FAT32.

FAT16
/fat siks-tEn/

The 16-bit version of the above FAT. Essentially, it is what writes the data to your hard disk. The difference between FAT16 and FAT32 is that the size of the clusters or blocks that it writes on your hard disk are larger, therefore alotting less space on the drive for writing information. Ex: an apple cut into ˝ inch pieces will yeild fewer pieces than an apple cut into Ľ inch pieces. You therefore have less space to write your data, and can only fit 1.99 Gig in each partition.

FAT32
/fat thir-tE-too/

The 32-bit version of the above FAT. Essentially, it is what writes the data to your hard disk. The difference between FAT32 and FAT16 is that the size of the clusters or blocks that it writes to your hard disk are smaller, therefore alotting more space on the drive for writing information. Ex: an apple cut into Ľ inch pieces will yeild more pieces than an apple cut into ˝ inch pieces. You therefore have more space to write your data, and can only fit 7.99 Gig in each partition without troubles, even though Microsoft maintains that the size limit is infinite.

Firewall
/fI-er wol/

A system designed to prevent unauthorized access to or from a private network. Firewalls can be implemented in both hardware and software, or a combination of both. Firewalls are frequently used to prevent unauthorized Internet users from accessing private networks connected to the Internet, especially intranets. All messages entering or leaving the intranet pass through the firewall, which examines each message and blocks those that do not meet the specified security criteria. There are several types of firewall techniques:

Packet filter: Looks at each packet entering or leaving the network and accepts or rejects it based on user-defined rules. Packet filtering is fairly effective and transparent to users, but it is difficult to configure. In addition, it is susceptible to IP spoofing. Application gateway: Applies security mechanisms to specific applications, such as FTP and Telnet servers. This is very effective, but can impose a performance degradation.

Circuit-level gateway: Applies security mechanisms when a TCP or UDP connection is established. Once the connection has been made, packets can flow between the hosts without further checking.

Proxy server: Intercepts all messages entering and leaving the network. The proxy server effectively hides the true network addresses. In practice, many firewalls use two or more of these techniques in concert.

A firewall is considered a first line of defense in protecting private information. For greater security, data can be encrypted.

Frame Relay
/frAm rElA/

This is a cost effective, lightweight, many-to-many, medium speed, virtual network, link-layer technology. Frame relay is supported by almost all exchange carriers (telco's), and most of the private networks of some ISP's. It's tunable, too; bandwidths are a function of the protocol and can be changed repeatedly over the life of the circuit.

FTP - File Transfer Protocol
/ef tE pE/ or /fi-el chranz-fer prO-tO-col/

The File Transfer Protocol (FTP) was the standard means for transfer of files on the Internet before the advent of the HyperText Transfer Protocol (HTTP) and the World Wide Web. Although many of its functions have been taken over by the HTTP protocol, FTP is still used extensively for file transfer on the Internet.
The FTP protocol is, like Telnet, an old one. It still gets extensive use, though many anonymous FTP sites are being replaced with corresponding Web sites, and it is now common to access even FTP sites with a Web browser rather than with a separate FTP program.
The most extensive modern usage of FTP is to transfer files between one networked computer and another where the user has accounts. This is quite analogous to anonymous FTP, except that you have to login with a user name and password. For example, the transfer of files from Web development sites to Web servers is often accomplished with FTP. A more extensive introduction to the FTP protocol may be found in Zen and the Art of the Internet.

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G

Gateway
/gAt-wA/

In networking, a combination of hardware and software that links two different types of networks. Gateways between e-mail systems, for example, allow users on different e-mail systems to exchange messages.

GIF- Graphics Interchange Format
/jif/ or /graf-iks in-ter-chanj for-mat/

GIF, which stands for Graphics Interchange Format, is a lossless method of compression. All that means is that when the program that creates a GIF squashes the original image down it takes care not to lose any data. It uses a simple substitution method of compression. If the algorithm comes across several parts of the image that are the same, say a sequence of digits like this, 1 2 3 4 5, 1 2 3 4 5, 1 2 3 4 5, it makes the number 1 stand for the sequence 1 2 3 4 5 so that you could render the same sequence 1 1 1, obviously saving a lot of space. It stores the key to this (1 = 1 2 3 4 5) in a hash table, which is attached to the image so that the decoding program can unscramble it.

The maximum compression available with a GIF therefore depends on the amount of repetition there is in an image. A flat colour will compress well - sometimes even down to one tenth of the original file size - while a complex, non-repetitive image will fare worse, perhaps only saving 20% or so.

There are problems with GIFs. One is that they are limited to a palette of 256 colours or less. Compuserve, which created the GIF, did at one point say it would attempt to produce a 24-bit version of the GIF, but then along came problem number two: Unisys. Unisys discovered that it owned some patents to key parts of the GIF compression technology, and has started demanding fees from every company whose software uses the (freely available) GIF code. This has somewhat stifled development.

There is a 24-bit, license-free GIFalike called the PNG format, but this has yet to take off.

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H

HDLC
/Atch dE ell sE/

Both a point-to-point and multi-party link-layer technology, HDLC provides reliable, acknowledged transfer across dedicated links.

Host
/hOst/

(n) (1) A computer system that is accessed by a user working at a remote location. Typically, the term is used when there are two computer systems connected by modems and telephone lines. The system that contains the data is called the host, while the computer at which the user sits is called the remote terminal.
(2) A computer that is connected to a TCP/IP network, including the Internet. Each host has a unique IP address.
(v) To provide the infrastructure for a computer service. For example, there are many companies that host Web servers. This means that they provide the hardware, software, and communications lines required by the server, but the content on the server may be controlled by someone else.

HTML - HyperText Markup Language
/Ach tE em el/ or /hI-per-tekst mar-kup lAng-wedj/

HTML is the authoring language used to create documents on the World Wide Web. HTML is similar to SGML, although it is not a strict subset.

HTTP - HyperText Transfer Protocol
/Ach tE tE pE/ or /hI-per-tekst chranz-fer prO-tO-col/
HTTP is the underlying protocol used by the World Wide Web. HTTP defines how messages are formatted and transmitted, and what actions Web servers and browsers should take in response to various commands. For example, when you enter a URL in your browser, this actually sends an HTTP command to the Web server directing it to fetch and transmit the requested Web page. The other main standard that controls how the World Wide Web works is HTML, which covers how Web pages are formatted and displayed. HTTP is called a stateless protocol because each command is executed independently, without any knowledge of the commands that came before it. This is the main reason that it is difficult to implement Web sites that react intelligently to user input. This shortcoming of HTTP is being addressed in a number of new technologies, including ActiveX, Java, JavaScript and cookies. Currently, most Web browsers and servers support HTTP 1.1. One of the main features of HTTP 1.1 is that it supports persistent connections. This means that once a browser connects to a Web server, it can receive multiple files through the same connection. This should improve performance by as much as 20%.

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I

Intranet
/in-chruh-net/

A network based on TCP/IP protocols (an internet) belonging to an organization, usually a corporation, accessible only by the organization's members, employees, or others with authorization. An intranet's Web sites look and act just like any other Web sites, but the firewall surrounding an intranet fends off unauthorized access. Like the Internet itself, intranets are used to share information. Secure intranets are now the fastest-growing segment of the Internet because they are much less expensive to build and manage than private networks based on proprietary protocols.

IP - Internet Protocol
/I pE/ or /in-ter-net prO-tO-col/

IP is pronounced as two separate letters. IP specifies the format of packets, also called datagrams, and the addressing scheme. Most networks combine IP with a higher-level protocol called Transport Control Protocol (TCP), which establishes a virtual connection between a destination and a source. IP by itself is something like the postal system. It allows you to address a package and drop it in the system, but there's no direct link between you and the recipient. TCP/IP, on the other hand, establishes a connection between two hosts so that they can send messages back and forth for a period of time. The current version of IP is IPv4. A new version, called IPv6 or IPng, is under development.

IP Address
/I pE uh-jres/

An identifier for a computer or device on a TCP/IP network. Networks using the TCP/IP protocol route messages based on the IP address of the destination. The format of an IP address is a 32-bit numeric address written as four numbers separated by periods. Each number can be zero to 255. For example, 1.160.10.240 could be an IP address. Within an isolated network, you can assign IP addresses at random as long as each one is unique. However, connecting a private network to the Internet requires using registered IP addresses (called Internet addresses) to avoid duplicates. The four numbers in an IP address are used in different ways to identify a particular network and a host on that network. The InterNIC Registration Service assigns Internet addresses from the following three classes.

Class A - supports 16 million hosts on each of 127 networks

Class B - supports 65,000 hosts on each of 16,000 networks

Class C - supports 254 hosts on each of 2 million networks

The number of unassigned Internet addresses is running out, so a new classless scheme called CIDR is gradually replacing the system based on classes A, B, and C and is tied to adoption of IPv6.

IPX/SPX - Internetwork Packet Exchange, Sequenced Packet Exchange
/eye pE ex es pE ex/

Short for Internetwork Packet Exchange, IPX is a networking protocol used by the Novell NetWare operating systems. Like UDP/IP, IPX is a datagram protocol used for connectionless communications. Higher-level protocols, such as SPX and NCP, are used for additional error recovery services.

The successor to IPX is the NetWare Link Services Protocol (NLSP).

Short for Sequenced Packet Exchange, SPX is a transport layer protocol (layer 4 of the OSI Model) used in Novell Netware networks. The SPX layer sits on top of the IPX layer (layer 3) and provides connection-oriented services between two nodes on the network. SPX is used primarily by client/server applications.

Whereas the IPX protocol is similar to IP, SPX is similar to TCP. Together, therefore, IPX/SPX provides connection services similar to TCP/IP.

IRC - Internet Relay Chat
/I ar sE/ or /in-ter-net rE-lA chat/

IRC is a chat system developed by Jarkko Oikarinen in Finland in the late 1980s. IRC has become very popular as more people get connected to the Internet because it enables people connected anywhere on the Internet to join in live discussions. Unlike older chat systems, IRC is not limited to just two participants. To join an IRC discussion, you need an IRC client and Internet access. The IRC client is a program that runs on your computer and sends and receives messages to and from an IRC server. The IRC server, in turn, is responsible for making sure that all messages are broadcast to everyone participating in a discussion. There can be many discussions going on at once; each one is assigned a unique channel.

ISA - Industry Standard Architecture
/I es A/ or /in-dus-tree stan-derd ark-i-tek-chur/

The bus architecture used in the IBM PC/XT and PC/AT. It's often abbreviated as ISA (pronounced as separate letters or as eye-sa) bus. The AT version of the bus is called the AT bus and became a de facto industry standard. Starting in the early 90s, ISA began to be replaced by the PCI local bus architecture. Most computers made today include both an AT bus for slower devices and a PCI bus for devices that need better bus performance. In 1993, Intel and Microsoft introduced a new version of the ISA specification called Plug and Play ISA. Plug and Play ISA enables the operating system to configure expansion boards automatically so that users do not need to fiddle with DIP switches and jumpers.

ISDN - Integrated Services Digital Network
/I es dE en/ or /in-te-grA-ted sir-ves-ez dij-i-tuhl net-werk/

ISDN is an international communications standard for sending voice, video, and data over digital telephone lines. ISDN requires special metal wires and supports data transfer rates of 64 Kbps (64,000 bits per second). Most ISDN lines offered by telephone companies give you two lines at once, called B channels. You can use one line for voice and the other for data, or you can use both lines for data to give you data rates of 128 Kbps, three times the data rate provided by today's fastest modems. The original version of ISDN employs baseband transmission. Another version, called B-ISDN, uses broadband transmission and is able to support transmission rates of 1.5 Mbps. B-ISDN requires fiber optic cables and is not widely available.

ISP - Internet Service Provider
/I es pE/ or /in-ter-net sir-ves prO-vI-dir/

An ISP is a company that provides access to the Internet. For a monthly fee, the service provider gives you a software package, username, password and access phone number. Equipped with a modem, you can then log on to the Internet and browse the World Wide Web and USENET, and send and receive e-mail. In addition to serving individuals, ISPs also serve large companies, providing a direct connection from the company's networks to the Internet. ISPs themselves are connected to one another through Network Access Points (NAPs).

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J

Java
/jo-vuh/

A high-level programming language developed by Sun Microsystems. Java was originally called OAK, and was designed for handheld devices and set-top boxes. Oak was unsuccessful so in 1995 Sun changed the name to Java and modified the language to take advantage of the burgeoning World Wide Web. Java is an object-oriented language similar to C++, but simplified to eliminate language features that cause common programming errors. Java source code files (files with a .java extension) are compiled into a format called bytecode (files with a .class extension), which can then be executed by a Java interpreter. Compiled Java code can run on most computers because Java interpreters and runtime environments, known as Java Virtual Machines (VMs), exist for most operating systems, including UNIX, the Macintosh OS, and Windows. Bytecode can also be converted directly into machine language instructions by a just-in-time compiler (JIT). Java is a general purpose programming language with a number of features that make the language well suited for use on the World Wide Web. Small Java applications are called Java applets and can be downloaded from a Web server and run on your computer by a Java-compatible Web browser, such as Netscape Navigator or Microsoft Internet Explorer.

JavaScript
/jo-vuh-skript/

A scripting language developed by Netscape to enable Web authors to design interactive sites. Although it shares many of the features and structures of the full Java language, it was developed independently. Javascript can interact with HTML source code, enabling Web authors to spice up their sites with dynamic content. JavaScript is endorsed by a number of software companies and is an open language that anyone can use without purchasing a license. It is supported by recent browsers from Netscape and Microsoft, though Internet Explorer supports only a subset, which Microsoft calls Jscript.

JPG
/jA-peg/

see JPEG for further information about this file type, which is just a shortened version of the JPEG file type, shortened so that it can be more easily read by Windows.

JPEG
/jA-peg/

JPEG, an image compression standard sanctioned by the ISO (International Standards Organization), gives users the ability to take an image and compress it with little or no noticeable quality degradation. The original image is taken through a series of steps, (initial input, Discrete Cosine Transform, quantizat ion, and enc oding) each of which contributes to the overall compression of the image. Compression ratios for a 24-bit color image can be as high as 100:1! At that ratio, however, there is noticeable image degradation, even at normal magnification. Usual image compression ranges from 10:1 to as high as 20:1 without any visible image degradation

JPEG is also a lossy compression method. In other words, to save space it just throws away parts of an image. Obviously you can't just go around discarding any old piece of information so what the JPEG algorithm does is first divide the image into squares (you can see these squares on badly-compressed JPEGs).

It then uses a piece of mathematics called Discrete Cosine Transformation to turn the square of data into a set of curves, some small, some big, that go together to make up the image. This is where the lossy bit comes in: depending on how much you want to compress the image the algorithm throws away the less significant part of the data (the smaller curves) which adds less to the overall "shape" of the image. This means that, unlike GIF, you get a say in how much you want to compress an image by. However the lossy compression method can generate artifacts - unwanted effects such as false colour and blockiness - if not used carefully.

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K

There are no definitions for the letter 'K'

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L

LAN - Local Area Network
/lan/ or /lO-kuhl ar-E-uh net-werk/

A computer network that spans a relatively small area. Most LANs are confined to a single building or group of buildings. However, one LAN can be connected to other LANs over any distance via telephone lines and radio waves. A system of LANs connected in this way is called a wide-area network (WAN). Most LANs connect workstations and personal computers. Each node (individual computer ) in a LAN has its own CPU with which it executes programs, but it is also able to access data and devices anywhere on the LAN. This means that many users can share expensive devices, such as laser printers, as well as data. Users can also use the LAN to communicate with each other, by sending e-mail or engaging in chat sessions. There are many different types of LANs Ethernets being the most common for PCs. Most Apple Macintosh networks are based on Apple's AppleTalk network system, which is built into Macintosh computers. The following characteristics differentiate one LAN from another:

topology : The geometric arrangement of devices on the network. For example, devices can be arranged in a ring or in a straight line.

protocols : The rules and encoding specifications for sending data. The protocols also determine whether the network uses a peer-to-peer or client/server architecture.

media : Devices can be connected by twisted-pair wire, coaxial cables, or fiber optic cables. Some networks do without connecting media altogether, communicating instead via radio waves.

LANs are capable of transmitting data at very fast rates, much faster than data can be transmitted over a telephone line; but the distances are limited, and there is also a limit on the number of computers that can be attached to a single LAN.

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M

MBR - Master Boot Record
/em bE ar/ or /mas-ter boot rek-erd/

The master boot record is a small program that is executed when a computer boots up. Typically, the MBR resides on the first sector of the hard disk. The program begins the boot process by looking up the partition table to determine which partition to use for booting. It then transfers program control to the boot sector of that partition, which continues the boot process. In DOS and Windows systems, you can create the MBR with the FDISK /MBR command. A MBR virus is a common type of virus that replaces the MBR with its own code. Since the MBR executes every time a computer is started, this type of virus is extremely dangerous. MBR viruses normally enter a system through a floppy disk that is installed in the floppy drive when the computer is started up. Even if the floppy disk is not bootable, it can infect the MBR.

MIDI - Musical Instrument Digital Interface
/mi-dE/ or mU-zi-kul in-struh-ment dij-i-tul in-ter-fAs/

MIDI (Musical Instrument Digital Interface) is a protocol designed for recording and playing back music on digital synthesizers that is supported by many makes of personal computer sound cards. Originally intended to control one keyboard from another, it was quickly adopted for the personal computer. Rather than representing musical sound directly, it transmits information about how music is produced. The command set includes note-ons, note-offs, key velocity, pitch bend and other methods of controlling a synthesizer. The sound waves produced are those already stored in a wavetable in the receiving instrument or sound card.

Since a MIDI file only represents player information, it is far more concise than formats that the sound directly. An advantage is very small file size. A disadvantage is the lack of specific sound control.

With a program that provides this interface, you can create music using a standard keyboard or other input device. You or others can then play your MIDI-conforming creation with the same or another program and a sound card as a music synthesizer. The MIDI program may come with a graphical user interface that looks like a sound studio control room. Many sound cards come as a package with MIDI software (for example, Media Vision's Pro Audio Studio 16).

The MIDI protocol uses eight-bit serial transmission with one start bit and one stop bit, has a 31.25 Kbs data rate, and is asynchronous. Connection is made through a five-pin DIN plug, of which three pins are used.

MIME - Multipurpose Internet Mail Extensions
/mIm/ or /mul-tE-per-pus in-ter-net mAl ex-ten-shunz/

MIME is a specification for formatting non-ASCII messages so that they can be sent over the Internet. Many e-mail clients now support MIME, which enables them to send and receive graphics, audio, and video files via the Internet mail system. In addition, MIME supports messages in character sets other than ASCII. There are many predefined MIME types, such as GIF graphics files and PostScript files. It is also possible to define your own MIME types. In addition to e-mail applications, Web browsers also support various MIME types. This enables the browser to display or output files that are not in HTML format. MIME was defined in 1992 by the Internet Engineering Task Force (IETF). A new version, called S/MIME, supports encrypted messages.

MMX - Multimedia Extensions
/em em ex/ or /mul-tE-mE-dE-uh ex-ten-shunz/

A set of 57 multimedia instructions built into Intel's newest microprocessors and other x86-compatible microprocessors. MMX-enabled microprocessors can handle many common multimedia operations, such as digital signal processing (DSP), that are normally handled by a separate sound or video card. However, only software especially written to call MMX instructions -- so-called MMX-enabled software -- can take advantage of the MMX instruction set. The first generation of computers with MMX chips hit the market in January, 1997.

MOV - Quick Time MOVie
/em Oh vE/ or /kwik tIm moo-vE/
A file type used mostly by windows and/or macintosh to view full motion movies/trailers, etc...

(1) (Metal Oxide Varistor) A discrete electronic component that diverts excessive voltage to the ground and/or neutral lines. See MOV surge suppression.

(2) An assembly language instruction that moves (copies) data from one location to another. See move.

(3) Movie (QuickTime for Microsoft Windows), also (AutoCAD/AutoFlix)

MPEG - Moving Picture Experts Group
/em-peg/ or /moo-vEng pik-chur ex-perts groop/

MPEG is a working group of ISO. The term also refers to the family of digital video compression standards and file formats developed by the group. MPEG generally produces better-quality video than competing formats, such as Video for Windows, Indeo and QuickTime. MPEG files can be decoded by special hardware or by software. MPEG achieves high compression rate by storing only the changes from one frame to another, instead of each entire frame. The video information is then encoded using a technique called DCT. MPEG uses a type of lossy compression, since some data is removed. But the diminishment of data is generally imperceptible to the human eye. There are two major MPEG standards: MPEG-1 and MPEG-2. The most common implementations of the MPEG-1 standard provide a video resolution of 352-by-240 at 30 frames per second (fps). This produces video quality slightly below the quality of conventional VCR videos. A newer standard, MPEG-2, offers resolutions of 720x480 and 1280x720 at 60 fps, with full CD-quality audio. This is sufficient for all the major TV standards, including NTSC, and even HDTV. MPEG-2 is used by DVD-ROMs. MPEG-2 can compress a 2 hour video into a few gigabytes. While decompressing an MPEG-2 data stream requires only modest computing power, encoding video in MPEG-2 format requires significantly more processing power. The ISO standards body is currently working on a new version of MPEG called MPEG-4 (there is no MPEG-3). MPEG-4 will be based on the QuickTime file format.

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N

NetBEUI NetBios Enhanced User Interface
/net-boo-E/

Netbeui is an enhanced version of the NetBIOS protocol used by network operating systems such as LAN Manager, LAN Server, Windows for Workgroups, Windows 95 and Windows NT.

Netbeui was originally designed by IBM for their Lan Manager server and later extended by Microsoft and Novell.

NTFS - NT File System
/en tE ef es/ or /en tE fI-el sis-tem/

Short for NT File System, one of the file system for the Windows NT operating system (Windows NT also supports the FAT file system). NTFS has features to improve reliability, such as transaction logs to help recover from disk failures. To control access to files, you can set permissions for directories and/or individual files. NTFS files are not accessible from other operating systems such as DOS.

For large applications, NTFS supports spanning volumes, which means files and directories can be spread out across several physical disks.

NLSP NetWare Link Services Protocol
/en el es pE/

Function Unknown.

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O

OLE - Object Linking and Embedding
/Oh-lA/ or /ob-jekt lEnk-Eng and em-bed-Eng/

OLE is a compound document standard developed by Microsoft Corporation. It enables you to create objects with one application and then link or embed them in a second application. Embedded objects retain their original format and links to the application that created them. Support for OLE is built into the Windows and Macintosh operating systems. A competing compound document standard developed jointly by IBM, Apple Computer, and other computer firms is called OpenDoc.

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P

PAP - Password Authentication Protocol
/pap/

PAP is the most basic form of authentication, in which a user's name and password are transmitted over a network and compared to a table of name-password pairs. Typically, the passwords stored in the table are encrypted. The Basic Authentication feature built into the HTTP protocol uses PAP. The main weakness of PAP is that both the username and password are transmitted "in the clear" -- that is, in an unencrypted form. Contrasts with CHAP.

PCI - Peripheral Component Interconnect
/pE sE I/ or /per-if-er-uhl cum-pO-nent in-ter-cun-ekt/

PCI is a local bus standard developed by Intel Corporation. Most modern PCs include a PCI bus in addition to a more general ISA expansion bus. Many analysts, however, believe that PCI will eventually supplant ISA entirely. PCI is also used on newer versions of the Macintosh computer. PCI is a 64-bit bus, though it is usually implemented as a 32-bit bus. It can run at clock speeds of 33 or 66 MHz. At 32 bits and 33 MHz, it yields a throughput rate of 133 MBps. Although it was developed by Intel, PCI is not tied to any particular family of microprocessors.

PCMCIA - Personal Computer Memory Card International Association
/pE sE em sE I A/ or /per-sun-uhl cum-pU-ter mem-or-E card in-ter-na-shun-uhl uh-sO-sE-A-shun/

PCMCIA is an organization consisting of some 500 companies that has developed a standard for small, credit card-sized devices, called PC Cards. Originally designed for adding memory to portable computers, the PCMCIA standard has been expanded several times and is now suitable for many types of devices. There are in fact three types of PCMCIA cards. All three have the same rectangular size (85.6 by 54 millimeters), but different widths

Type I cards can be up to 3.3 mm thick, and are used primarily for adding additional ROM or RAM to a computer.

Type II cards can be up to 5.5 mm thick. These cards are often used for modem and fax modem cards.

Type III cards can be up to 10.5 mm thick, which is sufficiently large for portable disk drives.

As with the cards, PCMCIA slots also come in three sizes:

A Type I slot can hold one Type I card

A Type II slot can hold one Type II card or two Type I cards

A Type III slot can hold one Type III card or a Type I and Type II card.

In general, you can exchange PC Cards on the fly, without rebooting your computer. For example, you can slip in a fax modem card when you want to send a fax and then, when you're done, replace the fax modem card with a memory card.

Ping - Packet Internet Groper
/pEng/ or /pak-et in-ter-net grO-per/

Ping is a utility to determine whether a specific IP address is accessible. It works by sending a packet to the specified address and waiting for a reply. PING is used primarily to troubleshoot Internet connections. Ping can be ran from an msdos prompt by typing in "ping xxx.xxx.xxx.xxx" - where xxx.xxx.xxx.xxx is the IP address you want to test.

POP - Post Office Protocol or Point of Presence
/pop/ or /pOst of-is prO-tO-col or point uv prez-ents/

(1) POP (Post Office Protocol) is a protocol used to retrieve e-mail from a mail server. Most e-mail applications (sometimes called an e-mail client) use the POP protocol, although some can use the newer IMAP (Internet Message Access Protocol).
(2) PoP (Point of Presence), is a telephonenumber that gives you dial-up access. Internet Service Providers (ISPs) generally provide many PoPs so that users can make a local call to gain Internet access.

A point-of-presence (POP) is the location of an access point to the Internet. A POP necessarily has a unique Internet (IP) address. Your independent service provider (ISP) or online service provider (OSP) has a point-of-presence on the Internet. POPs are sometimes used as one measure of the size and growth of an ISP or OSP.
A POP may actually reside in rented space owned by a telecommunications carrier such as Sprint. A POP usually includes routers, digital/analog call aggregators, servers, and frequently frame relay or ATM switches.

POP3 Post Office Protocol Three
/pop-thrE/ or /pOst of-is prO-tO-col thrE/

There are two versions of POP. The first, called POP2, became a standard in the mid-80's and requires an SMTP server to send messages. The newer version, POP3, can be used with or without an SMTP server.

PPP - Point-to-Point Protocol
/pE pE pE/ or /point too point prO-tO-col/

PPP is a method of connecting a computer to the Internet. PPP is more stable than the older SLIP protocol and provides error checking features. PPP endpoints can negotiate network paramaters, and, optionally, can authenticate their peers as communications proceed.

Protocol
/prO-tO-col/

An agreed-upon format for transmitting data between two devices. The protocol determines the following:

the type of error checking to be used

data compression method, if any

how the sending device will indicate that it has finished sending a message

how the receiving device will indicate that it has received a message

There are a variety of standard protocols from which programmers can choose. Each has particular advantages and disadvantages; for example, some are simpler than others, some are more reliable, and some are faster. From a user's point of view, the only interesting aspect about protocols is that your computer or device must support the right ones if you want to communicate with other computers. The protocol can be implemented either in hardware or in software.

Proxy Server
/prok-sE sir-vir/

A server that sits between a client application, such as a Web browser, and a real server. It intercepts all requests to the real server to see if it can fulfill the requests itself. If not, it forwards the request to the real server. Proxy servers have two main purposes:

Improve Performance: Proxy servers can dramatically improve performance for groups of users. This is because it saves the results of all requests for a certain amount of time. Consider the case where both user X and user Y access the World Wide Web through a proxy server. First user X requests a certain Web page, which we'll call Page 1. Sometime later, user Y requests the same page. Instead of forwarding the request to the Web server where Page 1 resides, which can be a time-consuming operation, the proxy server simply returns the Page 1 that it already fetched for user X. Since the proxy server is often on the same network as the user, this is a much faster operation. Real proxy servers support hundreds or thousands of users. The major online services such as Compuserve and America Online, for example, employ an array of proxy servers.

Filter Requests: Proxy servers can also be used to filter requests. For example, a company might use a proxy server to prevent its employees from accessing a specific set of Web sites.

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Q

There are no definitions for the letter 'Q'

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R

RAS - Remote Access Server
/raz/ or /rE-mOt ak-ses sir-vir/

RAS is a feature built into Windows NT that enables users to log into an NT-based LAN using a modem, X.25 connection or WAN link. RAS works with several major network protocols, including TCP/IP, IPX, and Netbeui. To use RAS from a remote node, you need a RAS client program, which is built into most versions of Windows, or any PPP client software. For example, most remote control programs work with RAS.

RIP
/rip/

Known only to a few as the Routing Information Protocol, it is a Distance Vector Protocol that uses hop count as its metric. RIP is widely used for routing traffic in the global Internet and is an interior gateway protocol (IGP), which means that it performs routing within a single autonomous system. For more information check out This Cisco Page

Router
/r-OW-ter/ or /r-eww-ter/

A router is a device that routes traffic through a network, weather that be an internal LAN or an external WAN. Routers use headers and a forwarding table to determine where packets go, and they use ICMP to communicate with each other and configure the best route between any two hosts. Very little data filtering is actually done through a router, as they generally don't care about the type of data they handle.

Routing Table
/r-OW-tEng tAbull/ or /r-eww-tEng tAbull/

A routing table is a list that a router keeps that tells it "where to go next"

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