Anycast
In Internet Protocol Version 6 (IPv6), anycast is communication between a single sender and the nearest of several receivers in a group. The term exists in contradistinction to multicast, communication between a single sender and multiple receivers, and unicast, communication between a single sender and a single receiver in a network.
Anycasting is designed to let one host initiate the efficient updating of router tables for a group of hosts. IPv6 can determine which gateway host is closest and sends the packets to that host as though it were a unicast communication. In turn, that host can anycast to another host in the group until all routing tables are updated.
Apache
Apache is a freely available Web server that is distributed under an "open source” license. Version 2.0 runs on most UNIX-based operating systems (such as Linux, Solaris, Digital UNIX, and AIX), on other UNIX/POSIX-derived systems (such as Rhapsody, BeOS, and BS2OOO/OSD), on AmigaOS, and on Windows 2000. According to the Netcraft (www.netcraft.com) Web server survey in February, 2001, 60% of all Web sites on the Internet are using Apache (62% including Apache derivatives), making Apache more widely used than all other Web servers combined. Apache complies with the newest level of the Hypertext Transport Protocol, HTTP 1.1. Free support is provided through a bug reporting system and several Usenet newsgroups. Several companies offer priced support.
APL
APL (A Programming Language) is a general-purpose, third-generation (3GL) programming language that allows certain data manipulations to be expressed with a special non-ASCII set of symbols, resulting in programs that are shorter than would be possible using most other languages. APL’s notation allows matrix manipulation as well as recursion functions to be built into simple expressions rather than requiring multiple language statements. APL is more frequently thought of as a language for scientific computation, but it can be used for other purposes as well. Programs can be developed interactively and are usually interpreted rather than compiled. The special symbols require keyboard support and specific editors so that the symbols can be displayed and printed.
apogee
When a satellite follows a non-circular orbit around the earth, the satellite’s path is an ellipse with the center of the earth at one focus. Such a satellite has variable altitude and variable orbital speed. The point of highest altitude is called apogee. The term also applies to the maximum distance in kilometers or miles between the satellite and the center of the earth. (Apogee can be measured between the satellite and the earth’s surface, although this is a less precise specification because the earth is not a perfect sphere. The difference is approximately 4,000 miles or 6,400 kilometers.)
At apogee, a satellite travels more slowly than at any other point in its orbit. When viewed from the earth’s surface, a satellite at or near apogee takes a long time to traverse the sky. In communications, apogee is the best time to access a satellite. Although its distance means that the signal path is long, the fact that the satellite is slowly moving means that it is accessible for a comparatively long time. In addition, if a directional antenna is used at a ground-based station, it is relatively easy to track the satellite because the position of the antenna (azimuth and elevation) need not be adjusted very often or rapidly.
One of the principal advantages of a geostationary satellite is the fact that it follows a circular orbit, so the orbital speed is constant. In addition, the satellite’s synchronization with the earth’s orbit means that the antenna of an earth-based station can be pointed at a fixed spot in the sky, and no further adjustment of antenna orientation is needed.
Compare perigee.
Apparent power
Apparent power is a measure of alternating current (AC) power that is computed by multiplying the root-mean-square (rms) current by the root-mean-square voltage. In a direct current (DC) circuit, or in an AC circuit whose impedance is a pure resistance, the voltage and current are in phase, and the following formula holds: P = F I
P Frms1rms
where P is the power in watts, Frms is the root-mean-square (rms) voltage in volts, and Irms is the rms current in amperes. But in an AC circuit whose impedance consists of reactance as well as resistance, the voltage and current are not in phase. This complicates the determination of power.
In an AC circuit, the product of the rms voltage and the rms current is called apparent power. When the impedance is a pure resistance, the apparent power is the same as the true power. But when reactance exists, the apparent power is greater than the true power. The vector difference between the apparent and true power is called reactive power.
If Pa represents the apparent power in a complex AC circuit, Pt represents the true power, and Pr represents the reactive power, then the following equation holds:
Pa2 = Pt2 + Pr2
APPC
APPC (Advanced Program-to-Program Communication, sometimes called LU 6.2) is a communication protocol and programming interface standard that operates in the presentation layer (the layer that ensures that messages are in the proper format for the recipient) and the session layer (the layer responsible for setting up and taking down the association of the two end points in a connection) of the Open Systems Interconnection (OSI) communications model. Originally developed by IBM as a remote transaction processing tool, APPC is now used to provide distributed services within a heterogeneous computing environment.
APPC software enables high-speed communication to take place between programs residing on different computers, and between workstations and midrange and mainframe computer servers. APPC is an open standard that is supported on most platforms.
APPC is based on IBM’s Systems Network Architecture (SNA).
Apple attachment unit interface_
Appleshare
The AppleShare protocol is a communications protocol from Apple Computer that allows client applications in a computer to exchange files with and request services from server programs in a computer network. AppleShare can be used over the Internet on top of the TCP/IP protocol, or on top of other network protocols such as Internetwork Packet Exchange and AppleTalk. Using the AppleShare protocol, a user can access files, applications, printers, and other resources on a remote server. It can communicate with any server program that is set up to receive an AppleShare client request.
All Macintosh and Mac OS clones include client and server AppleShare protocol support. Microsoft Windows NT Server and Novell NetWare both provide AppleShare server protocol support, although they currently only support AppleShare over AppleTalk. Third-party AppleShare client/server support is available for Microsoft Windows for Workgroups, Windows 95, and Windows NT, as well as for UNIX systems.
A given client and server may implement different sets of AppleShare protocol variations. The set of protocols to be used is negotiated before starting a session.
applet
An applet is a little application. Prior to the World Wide Web, the built-in writing and drawing programs that came with Windows were sometimes called "applets." On the Web, using Java, the object-oriented programming language, an applet is a small program that can be sent along with a Web page to a user. Java applets can perform interactive animations, immediate calculations, or other simple tasks without having to send a user request back to the server.
AppleTalk
AppleTalk is a set of local area network communication protocols originally created for Apple computers. An AppleTalk network can support up to 32 devices and data can be exchanged at a speed of 230.4 kilobits per second (Kbps). Devices can be as much as 1,000 feet apart. AppleTalk’s Datagram Delivery Protocol corresponds closely to the Network layer of the Open Systems Interconnection (OSI) communication model.
AppleTalk Address Resolution Protocol
appliance
An appliance or "network appliance” is a term used to denote a relatively low-cost PC designed for Internet access and specialized business use, but without the capabilities of a fully-equipped PC.
application
1) In information technology, an application is the use of a technology, system, or product.
2) The term application is a shorter form of application program. An application program is a program designed to perform a specific function directly for the user or, in some cases, for another application program. Examples of applications include word processors, database programs, Web browsers, development tools, drawing, paint, image editing programs, and communication programs. Applications use the services of the computer’s operating system and other supporting applications. The formal requests and means of communicating with other programs that an application program uses is called the application program interface (API).
application integration
Application integration is the process of bringing data or a function from one application program together with that of another application program. Object-oriented programming technology makes application integration easier to achieve. With traditional procedural programming, "bridge" programs had to be written so that one program could work with data or the output from functions in another program. The introduction of program "objects" such as Windows OCX and ActiveX controls provide standard interfaces so that objects designed for use in one application can be reused in other applications. Some software houses have developed programs that exploit this object technology so that you can have data or functions (object components or "controls") from one application (such as a word processor) be recognized by another application (such as a spreadsheet program). The result of integration may be a new application with its own user interface or the capability of a desktop or mainframe application to handle data and include capabilities borrowed from other applications.
Application layer
In the Open Systems Interconnection (OSI) communications model, the Application layer provides services for application programs that ensure that communication is possible. The Application layer is NOT the application itself that is doing the communication. It is a service layer that provides these services:
• Makes sure that the other party is identified and can be reached
• If appropriate, authenticates either the message sender or receiver or both
• Makes sure that necessary communication resources exist (for example, is there a modem in the sender’s computer?)
• Ensures agreement at both ends about error recovery procedures, data integrity, and privacy
• Determines protocol and data syntax rules at the application level. It may be convenient to think of the Application layer as the high-level set-up services for the application program or an interactive user.
application program
An application program (sometimes shortened to application) is any program designed to perform a specific function directly for the user or, in some cases, for another application program. Examples of application programs include word processors; database programs; Web browsers; development tools; drawing, paint, and image editing programs; and communication programs. Application programs use the services of the computer’s operating system and other supporting programs. The formal requests for services and means of communicating with other programs that a programmer uses in writing an application program is called the application program interface (API).
application program interface
An application program interface (API—and sometimes spelled application programming interface) is the specific method prescribed by a computer operating system or by an application program by which a programmer writing an application program can make requests of the operating system or another application.
An API can be contrasted with a graphical user interface or a command interface (both of which are direct user interfaces) as interfaces to an operating system or a program.
application server
An application server is a server program in a computer in a distributed network that provides the business logic for an application program. The application server is frequently viewed as part of a three-tier application, consisting of a graphical user interface (GUI) server, an application (business logic) server, and a database and transaction server. More descriptively, it can be viewed as dividing an application into:
1. A first-tier, front-end, Web browser-based graphical user interface, usually at a personal computer or workstation
2. A middle-tier business logic application or set of applications, possibly on a local area network or intranet server
3. A third-tier, back-end, database and transaction server, sometimes on a mainframe or large server
Older, legacy application databases and transaction management applications are part of the back end or third tier. The application server is the middleman between browser-based front-ends and back-end databases and legacy systems.
In many usages, the application server combines or works with a Web (Hypertext Transfer Protocol) server and is called a Web application server. The Web browser supports an easy-to-create HTML-based front-end for the user. The Web server provides several different ways to forward a request to an application server and to forward back a modified or new Web page to the user. These approaches include the Common Gateway Interface (CGI), FastCGI, Microsoft’s Active Server Page, and the Java Server Page. In some cases, the Web application servers also support request "brokering" interfaces such as CORBA Internet Inter-ORB Protocol (IIOP).
application service provider
ASP is also an abbreviation for Active Server Page. An application service provider (ASP) is a company that offers individuals or enterprises access over the Internet to applications and related services that would otherwise have to be located in their own personal or enterprise computers. Sometimes referred to as "apps-on-tap," ASP services are expected to become an important alternative, not only for smaller companies with low budgets for information technology, but also for larger companies as a form of outsourcing and for many services for individuals as well. Early applications include:
• Remote access serving for the users of an enterprise
• An off-premises local area network to which mobile users can be connected, with a common file server
• Specialized applications that would be expensive to install and maintain within your own company or on your own computer
Hewlett-Packard, SAP, and Qwest have formed one of the first major alliances for providing ASP services. They plan to make SAP’s popular R/3 applications available at "cybercenters" that will serve the applications to other companies. Microsoft is allowing some companies to offer its BackOffice products, including SQL Server, Exchange and Windows NT Server on a rental, pay-as-you-use basis. While ASPs are forecast to provide applications and services to small enterprises and individuals on a pay-per-use or yearly license basis, larger corporations are essentially providing their own ASP service in-house, moving applications off personal computers and putting them on a special kind of application server that is designed to handle the stripped-down kind of thin client workstation. This allows an enterprise to reassert the central control over application cost and usage that corporations formerly had in the period prior to the advent of the PC. Microsoft’s Terminal Server product and Citrix’s WinFrame products are leading thin-client application server products.
apps-on-tap
Apps-on-tap (short for "applications on tap") is computer industry jargon for application programs or other services (Hewlett-Packard calls them e-services) that are available online for businesses or consumers. (”On tap” is an idiomatic expression for "available.") The businesses that furnish apps-on-tap are called application service providers. The use of apps-on-tap is a form of outsourcing.
Aptent
Aptent (pronounced AP-tehnt, compounded from ‘application’ and ‘content’) is the combination of computer program applications with textual and graphic content on the Internet. The term was used by Tim Miller in an article on the subject in The Industry Standard magazine. Aptent, Miller observes, is increasingly what makes Web enterprises successful since it blends the capabilities of the computer and networking with the Web’s amazing capacity to amass content. Aptent is sometimes mostly programming, sometimes mostly content. Content is made available in new ways, arriving with programs that can interact with users, interpret and react to user behavior, send agents in search of content to be provided later, explode into more detailed content, allow users to develop their own content, and so forth. Advertisers and marketers, interested in ads and ideas that engage and involve, are also embracing aptent. Miller identifies some classes of aptent as: Search engines and directories. The original aptent providers, Yahoo, Excite, Lycos, Infoseek, and others scour the Web’s content and digest and index it so that users can access its millions of pages.
Communications aptent. E-mail and chat and discussion group sites and programming provide new ways for content to be created and exchanged. Important companies in communications aptent are Hotmail, WebChat Broadcasting, Parachat, Mirabilis, Silicon Investor, and Go2Net.
”Squirrel” aptent. Providing space where users can create their own personal home pages, address books, and special-event calendars, companies like GeoCities have brought users actively to the Web as full-time participants or at least allowed them to view the Web as a place to store their own content. Tripod and WhoWhere are other sites that let users create their own content.
Agent or "bot" aptent. These sites or applications allow users to gather information tailored to individual needs, compare prices at different online stores, and even discover or "mine" information that matches a user’s profile. Junglee, C2B, Quando, and Computer ESP are product examples.
Companies or Web sites that provide aptent rather than mere content tend to "scale" in terms of potential revenue and are attractive to angels, venture capitalists, and investors. Some aptent is able to self-proliferate, users spreading it to other users, a kind of viral marketing.
Aptent, Miller concludes, is still in its infancy. The message, he says, is "about doing things, not reading things.”
