Glossary (a-c)

10BaseT: A variant of Ethernet which allows stations to be attached via twisted pair cable and to communicate at 10Mb/s (adequate for WANs, which can't communicate any faster, and small LANs, but not for large LANs, for which the 100BaseT (fibre-optic) variant may be necessary). See also: Ethernet, Twisted pair, LAN, WAN.

Accessibility: This term refers to the extent to which the design of a website enables it to be viewed by visitors with various physical (sight, sound, movement, etc, etc) disabilities (I believe that very specific guidelines, and laws even, are provided on this subject in the USA - bless 'em; they do try - only joking!).

Acknowledgment (ACK): A type of message sent to indicate that a block of data arrived at its destination without error.

Active Server Pages: A server-side facility allowing User interaction via web pages.

AD: See: Administrative Domain.

Address: In the IT world, this term is used in various contexts. An example is the four octets IP address for a humble PC (qv) within the international and transparent DNS system. Another example is the Direct Memory Access (DMA) address in the memory of a PC allocated to a particular peripheral device's software driver. Other examples are the addresses of files in a PC's HDD or web-based database, e-mail addresses (qv) and MAC addresses (qv).

Address mask: A bit mask used to identify which bits in an IP address correspond to the network and subnet portions of the address. This mask is often referred to as the Subnet Mask because the network portion of the address can be determined by the encoding inherent in an IP address.

Address resolution: Conversion of an address, eg Internet address, into a corresponding physical location.

Administrative Domain (AD): A collection of hosts (qv) and routers (qv), and the interconnecting network(s) (qv), managed by a single administrative authority.

ADSL: Asynchronous Digital Subscriber Line. A standard Digital Subscriber Line (DSL) (qv) service in which download speeds are faster than (less-used) upload speeds, as opposed to a non-standard Synchronised Digital Subscriber Line (qv) in which the speeds are the same.

ADSL modem: The modem used to provide the (broadband) data transmission interface between a PC and the standard twisted-pair cable of a telephone line. See also Asynchronous Digital Subscriber Line, Broadband, Modem, Cable modem.

Alias: A name, usually short and easy to remember, that is translated into another name, usually long and difficult to remember.

American National Standards Institute (ANSI): The organization responsible for approving US standards in many areas, including computers and communications. Standards approved by this organization are often called ANSI standards, eg ANSI C is the version of the C language approved by ANSI. ANSI is a member of ISO. See also: International Organization for Standardization.

American Standard Code for Information Interchange (ASCII): A standard character-to-number encoding widely used in the computer industry. See also Byte.

Animation: Movement and/or other dynamic effects added to a displayed image.

Anonymous FTP: Anonymous FTP allows a user to retrieve documents, files, programs, and other archived data from anywhere in the Internet without having to establish a userID and password. By using the special userID of 'anonymous' the network user will bypass local security checks and will have access to publicly accessible files on the remote system. See also: Archive site and File Transfer Protocol.

ANSI: See: American National Standards Institute.

API: See: Application Program Interface.

Appletalk: A networking protocol developed by Apple Computers for communication between Apple Computer products, eg the Mac PC, and other computers. This protocol is independent of the network layer on which it is run. Implementations exist for Localtalk (a 235Kb/s LAN) and Ethertalk (a 10Mb/s LAN). See also Local Area Network.

Application: A program that performs a function directly for a user. FTP, mail and Telnet clients are examples of networking applications and a word processor is an example of an application that generates files.

Application layer: The top layer of the network protocol stack. The application layer is concerned with the semantics of work, eg formatting electronic mail messages. How to represent that data and how to reach the foreign node are issues for lower layers of the network.

Archie: A system to automatically gather, index and serve information on the Internet. The initial implementation of Archie provided an indexed directory of filenames from all anonymous FTP archives on the Internet. Later versions provide other collections of information. See also: Archive site, Gopher, Prospero, Wide Area Information Servers.

Archive site: A machine that provides access to a collection of files across the Internet, eg an 'anonymous FTP archive site' provides access to this material via FTP. See also: Anonymous FTP, Archie, Gopher, Prospero, Wide Area Information Servers.

ARP: See: Address Resolution Protocol.

ASCII: See: American Standard Code for Information Interchange.

ASP: See: Active Server Pages.

Authentication: The verification of the identity of a person or process.

Backbone: The top level in a hierarchical network. Stub and Transit networks which connect to the same backbone are guaranteed to be interconnected. See also: Stub network, Transit network.

Background: The general scene or surface against which designs, patterns, or figures are represented or viewed. On a webpage, it is what is behind the text and images.

Bandwidth: Relating to an Internet transmission channel, it is technically the difference, in Hertz (Hz), between the highest and lowest frequencies handled. However, as typically used, it is the speed, eg in Kb/s or Mb/s, at which data can be transmitted.

Banner: On interactive software, eg a website, a first screen containing a logo and/or author credits and/or a copyright notice. This is probably now the commonest sense.

Baseband: A transmission medium through which digital signals are sent without complicated frequency shifting. In general, only one communication channel is available at any given time. Ethernet is an example of a Baseband network. See also: Broadband, Ethernet.

Baud: Nominally a data transmission speed of 1 Byte/sec. See also Byte.

BBS: See: Bulletin Board System.

Binary: A numbering system to base 2, ie involving the use of '1' and '0', eg 11001001.

Binary digit (Bit): Each digit (with a value of '1' or '0') in a binary number.

BIOS: See Built-In Operating System.

Bit: See Binary digit.

Bookmarks: In an Internet browser other than MS Internet Explorer (see 'Favourites'), these are direct links to the URLs (qv) of often visited sites, saved in your browser for easy access. They help you keep track of websites you frequently visit and are considered by many to be the best thing about surfing the Web. By bookmarking a website while you visit it, you can easily return to it later via a couple of mouse clicks, rather than having to remember or type a very long or sometimes cryptic URL. In a Word Processor (qv), they can be hyperlinks (qv) to points in a document selected by the author of the document.

Boot: The process used to power-up and initialise a processor, eg a PC, from cold (analagous to 'pulling oneself up by one's own bootstrap'). See also Built-In Operating System.

Bounce: The return of a piece of e-mail to its sender because of an error in its delivery.

Bridge: A device which forwards traffic between network segments based on datalink layer information. These segments would have a common network layer address. See also: Gateway, Router.

Broadband: Relates to a data transmission medium that allows a wide range of frequencies (as opposed to Narrowband). It can carry multiple signals by dividing the total capacity of the medium into multiple, independent bandwidth channels, where each channel operates only on a specific range of frequencies. See also: Baseband.

Broadcast: A special type of multicast packet that all nodes on a network are always willing to receive.

Browser: The software Application on a PC that allows user-friendly surfing and viewing of websites on the Internet.

Buffer page: A webpage that appears after you click on an ad banner (instead of to the advertiser's homepage), further explaining the specifics of the ad offer. A Web designer may also create numerous buffer pages for one website and tailor each to adhere to the rules of a different search engine (to increase the site's ranking). Thus when a surfer does a search for a website concerned with a particular topic on one engine, that engine will index a buffer page that is customized for that engine (where the website has multiple buffer pages). When clicked on, a buffer page doesn't normally appear anywhere on the website itself; it only acts as an entry page that shows the search engine spiders code that will increase the site's chances for a higher ranking in search results. Note that buffer pages are not to be confused with splash pages (qv).

Built-In Operating System (BIOS): The battery-powered memory in a PC that boots it up when switched-on from cold. See also Boot.

Bulletin Board System (BBS): A computer, and associated software, which typically provides electronic messaging services, archives of files, and other services or activities to its visitors. Although BBSs have traditionally been the domain of hobbyists, an increasing number of BBSs are connected directly to the Internet, and many BBSs are currently operated by government, educational, and research institutions. See also: Electronic Mail, Internet, Usenet.

Byte: An eight-bit binary word, ie with values between decimal 0 and 255, eg as used in the ASCII representation of alpha-numeric characters. See also American Standard Code for Information Interchange.

Cable modem: The modem used to provide the (broadband) data transmission interface between a PC and the (wide bandwidth) coaxial cable laid by a cable TV company. See also Broadband, Modem, ADSL modem.

Capacity: In communications, it is the maximum possible data transfer rate of a communications channel under ideal conditions. The total capacity of a channel may be shared between several independent data streams using some kind of multiplexing, in which case, each stream's data rate may be limited to a fixed fraction of the total capacity.

Cascading Style Sheet (CSS): A file associated with the web pages in a website that avoids styles having to be set on every page. It is the essense of DHTML. See also Dynamic HyperText Mark-up Language.

CCITT: See: Comite Consultatif International de Telegraphique et Telephonique.

CD burner: The software Application on a PC that allows an installed CD writer drive to record onto CDR-W or blank CD-R media.

CD drive: Normally the CD player installed on all modern PCs, but includes optional CD writer drives.

Central Processing Unit (CPU): In a PC, it is the microprocessor plugged into its motherboard controlling all computer operations, eg one of Intel's Pentiums or one of AMD's Durons.

CGI: See Common Gateway Interface.

Character: In communications, this refers to an alpha-numeric or special character, represented by a byte (qv).

Checksum: A computed value that is dependent upon the contents of a packet (qv). This value is sent along with the packet when it is transmitted. The receiving system computes a new checksum based upon the received data and compares this value with the one sent. If the two values are the same, the receiver has a high degree of confidence that the data was received correctly.

Circuit switching: A communications paradigm in which a dedicated communication path is established between two hosts (qv), and on which all packets (qv) travel. The telephone system is an example of a circuit switched network. See also: Connection-oriented, Connectionless, Packet switching.

Client: A computer system or process that requests a service of another computer system or process. A workstation requesting the contents of a file from a file server is a client of the file server. See also: Client-server model, Server.

Client-server model: A common way to describe the paradigm of many network protocols. Examples include the name-server/name-resolver relationship in DNS and the file-server/file-client relationship in a NFS. See also: Client, Server, Domain Name System, Network File System.

Clout: A (slang) measure of the pressure an individual or organisation can effectively apply to produce a desired result in a defined area.

Code: In computing, the noun version of this word normally refers to the Assembly-level instructions a programmer has written into a program (C and C++, etc), webpage (HTML and JavaScript, etc) or script (.js, .asp, .php, etc). The verb version of the word is then equivalent to 'write'.

Codec: Coder-decoder. Typically relates to a multimedia file (coded in a particular format by the 'coder' part of a Codec and only usable when decoded by the 'decoder' part of the same type of Codec).

Comite Consultatif International de Telegraphique et Telephonique (CCITT): This organization is part of the United National International Telecommunications Union (ITU) and is responsible for making technical recommendations about telephone and data communications systems. Every four years the CCITT holds plenary sessions where they adopt new standards.

Common Gateway Interface (CGI): A protocol for programs that are used to produce on the fly content for browser delivery. Popular CGI programming languages include Perl, C, and PHP.

Congestion: Congestion occurs when the offered load exceeds the capacity of a data communication path.

Connection-oriented: The data communication method in which communication proceeds through three well-defined phases: connection establishment, data transfer, connection release. TCP is a connection-oriented protocol. See also: Circuit switching, Connectionless, Packet switching, Transmission Control Protocol.

Connectionless: The data communication method in which communication occurs between hosts (qv) with no previous setup. Packets (qv) between two hosts may take different routes, as each is independent of the other. UDP is a connectionless protocol. See also: Circuit switching, Connection-oriented, Packet switching, User Datagram Protocol.

Cookie: The name for a file stored on your hard drive by your Web browser and many websites that holds information about your browsing habits, eg what sites you have visited, which newsgroups you have read, etc. Many view 'cookies' as an invasion of privacy. These can be disabled within your browser Internet options.

Copyright: The legal right granted to an author, composer, playwright, publisher, or distributor to exclusive publication, production, sale, or distribution of a literary, musical, dramatic, or artistic work. This applies on the Internet as it does via any other media, but its enforcement is not easy and only invoked where big money is involved.

Counter: In the context of the Internet, a counter is a server-side script that counts the number of visitors to a URL (websit/page address). Counter quality and features can vary widely.

CPU: See Central Processing Unit.

CRC: See: Cyclic Redundancy Check.

CSS: See Cascading Style Sheet.

Cyberspace: A term coined by William Gibson in his fantasy novel Neuromancer to describe the media (sometimes called the 'ether') that allows communication between the 'world' of computers. Cyber is sometimes used as an adjective to associate an everyday pronoun with this almost virtual world, eg cyber-love (romance that is realised entirely via cyberspace).

Cyclic Redundancy Check (CRC): A number derived from a set of data that will be transmitted. By recalculating the CRC at the remote end and comparing it to the value originally transmitted, the receiving node can detect some types of transmission errors.