An ad-hoc network is a local area network or other small network, especially one with wireless or temporary plug-in connections, in which some of the network devices are part of the network only for the duration of a communications session or, in the case of mobile or portable devices, while in some close proximity to the rest of the network. In Latin, ad hoc literally means "for this," further meaning "for this purpose only," and thus usually temporary. The term has been applied to future office or home networks in which new devices can be quickly added, using, for example, the proposed Bluetooth technology in which devices communicate with the computer and perhaps other devices using wireless transmission.

One vendor offers an ad-hoc network technology that allows people to come to a conference room and, using infrared or radio frequency (RF) wireless signals, join their notebook computers with other conferees to a local network with shared data and printing resources. Each user has a unique network address that is immediately recognized as part of the network. The technology would also include remote users and hybrid wireless/wire connections.
 
 

AGP (Accelerated Graphics Port) is a bus specification that enables 3-D graphics to display quickly on ordinary personal computers. AGP is a special interface designed to convey 3-D images (for example, from Web sites or CD-ROMs) much more quickly and smoothly than is possible today on any computer other than an expensive graphics workstation. The interface uses your computer's main storage (RAM) for refreshing the monitor image and to support the texture mapping, z-buffering, and alpha blending required for 3-D image display. The AGP main memory use is dynamic, meaning that when not being used for accelerated graphics, main memory is restored to use by the operating system or other applications.

Intel, which has taken the lead in developing its specifications, has built AGP into a chipset for its Pentium II microprocessor. The newer, faster Pentium IIs are designed to work with the AGP chipset. Intel says the advanced floating point unit and faster cache algorithm of the Pentium II are better adapted for 3-dimensional applications.
 
 

ACPI (Advanced Configuration and Power Interface) is an industry specification for the efficient handling of power consumption in desktop and mobile computers. ACPI specifies how a computer's BIOS, operating system, and peripherals communicate with each other about power usage.

With ACPI, the following capabilities are possible (assuming the operating system supports them):

• The user can specify at what time a device, such as a display monitor, is to turn off or on.
• The user of a notebook computer can specify a lower-level of power consumption when the battery starts running low so that essential applications can still be used while other, less important applications are allowed to become inactive.
• The operating system can lower the clock speed during times when applications don't require the full processor clock speed.
• The operating system can reduce motherboard and peripheral device power needs by not activating devices until they are needed.
• The computer can enter a stand-by mode when no one is using it, but with modem power left on to receive incoming faxes.
• Devices can be plug-and-play. As soon as plugged in, they can be controlled by ACPI.

ACPI is in part a response to global concerns about energy conservation and environmental control. ACPI replaces Intel's SL technology and the more recent APM (Advanced Power Management) technology. Based on the collaborative effort of Intel, Toshiba, and Microsoft, ACPI moves away from power management that simply times out during inactivity to a more sophisticated demand-based power management. ACPI components collect information about power consumption from the computer and gives that information to the operating system. The operating system then distributes power to the different computer components on an as-needed basis. With ACPI, the computer can power itself down to a deep sleep state but still be capable of responding to an incoming phone call or a timed backup procedure. Another feature of ACPI is the "hibernation" mode. Before the computer goes into a deep sleep or hibernation, the contents of RAM are written to an image file and saved on the hard drive. When the computer is turned back on, the image file is reloaded, eliminating the need to reboot the system and open applications.
 
 

ActiveX is the name Microsoft has given to a set of "strategic" object-oriented program technologies and tools. The main technology is the Component Object Model (COM). Used in a network with a directory and additional support, COM becomes the Distributed Component Object Model (DCOM). The main thing that you create when writing a program to run in the ActiveX environment is a component, a self-sufficient program that can be run anywhere in your ActiveX network (currently a network consisting of Windows and Macintosh systems). This component is known as an ActiveX control. ActiveX is Microsoft's answer to the Java technology from Sun Microsystems. An ActiveX control is roughly equivalent to a Java applet.

If you have a Windows operating system on your personal computer, you may notice a number of Windows files with the "OCX" file name suffix. OCX stands for "Object Linking and Embedding control." Object Linking and Embedding (OLE) was Microsoft's program technology for supporting compound documents such as the Windows desktop. The Component Object Model now takes in OLE as part of a larger concept. Microsoft now uses the term "ActiveX control" instead of "OCX" for the component object.

One of the main advantages of a component is that it can be re-used by many applications (referred to as component containers). A COM component object (ActiveX control) can be created using one of several languages or development tools, including C++ and Visual Basic, or PowerBuilder, or with scripting tools such as VBScript.

Currently, ActiveX controls run in Windows 95/98/NT and in Macintosh. Microsoft plans to support ActiveX controls for UNIX.
 
 

ADSL (Asymmetric Digital Subscriber Line) is a technology for transmitting digital information at high bandwidths on existing phone lines to homes and businesses. ADSL is asymmetric in that it uses most of the channel to transmit downstream to the user and only a small part to receive information from the user. ADSL simultaneously accommodates analog (voice) information on the same line. ADSL is generally offered at downstream data rates from 512 Kbps to about 6 Mbps. A form of ADSL, known as Universal ADSL or G.Lite, has been initially approved as a standard by the ITU.

ADSL was specifically designed to exploit the one-way nature of most multimedia communication in which large amounts of information flow toward the user and only a small amount of interactive control information is returned. Several experiments with ADSL to real users began in 1996. In 1998, wide-scale installations began in several parts of the U.S. ADSL and other forms of DSL are expected to become more widely available in 1999 and 2000. With ADSL (and other forms of DSL), telephone companies are competing with cable companies and their cable modem services.
 
 

AMR (Audio/Modem Riser) is a specification developed by Intel for packaging the analogI/Oaudio functions of modem circuitry together with a codec chip (which converts back and forth from analog to digital) on a small board that plugs directly into a computer's motherboard. The small board is called a riser apparently because it rises above the motherboard rather than laying flatly on it. Having this circuitry on a riser means that it doesn't have to be part of the motherboard itself. Because getting certification for the manufacture of a new motherboard design is a lengthy process, removing this function from the motherboard provides more flexibility for manufacturers and allows advances in audio modem design to be implemented more easily. Another specification, MDC (Mobile Daughter Card) is the equivalent of AMR but for use in mobile computers.

In the past, an internal modem was installed in one of several slots inside the computer chassis and an external modem was plugged into a serial port at the rear of the computer. With AMR design, the slot can now be used for other purposes. The AMR card can also provide the foundation for higher-quality audio solutions such as 3D positional audio and better MIDI music production.
 
 

Anonymous e-mail is e-mail that has been directed to a recipient through a third-party server that does not identify the originator of the message.
 
 

Using the Internet's File Transfer Protocol (FTP), anonymous FTP is a method for giving users access to files so that they don't need to identify themselves to the server. Using an FTP program or the FTP command interface, the user enters "anonymous" as a user ID. Usually, the password is defaulted or furnished by the FTP server. Anonymous FTP is a common way to get access to a server in order to view or download files that are publicly available.

If someone tells you to use anonymous FTP and gives you the server name, just remember to use the word "anonymous" for your user ID. Usually, you can enter anything as a password.
 
 

An applet is a little application program. 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 is a set of communication protocols for Apple computers. AppleTalk's network-layer protocol corresponds closely to the Datagram Delivery Protocol of the Open Systems Interconnection (OSI) communication model.
 
 

This is the "official" name that ANSI group X3T10 uses for what the computer industry calls IDE (Integrated Drive Electronics).
 
 

ATAPI is an interface between your computer and attached CD-ROM drives and tape backup drives. Most of today's PC computers use the standard IDE (Integrated Drive Electronics) interface to address hard disk drives. ATAPI provides the additional commands needed for controlling a CD-ROM player or tape backup so that your computer can use the IDE interface and controllers to control these relatively newer device types.

ATAPI is part of the Enhanced IDE (EIDE) interface (also known as ATA-2).
 
 

ATM (asynchronous transfer mode) is a dedicated-connection switching technology that organizes digital data into 53-bytecells or packets and transmits them over a medium using digital signal technology. Individually, a cell is processed asynchronously relative to other related cells and is queued before being multiplexed over the line.

Because ATM is designed to be easily implemented by hardware (rather than software), faster processing speeds are possible. The prespecified bit rates are either 155.520 Mbps or 622.080 Mpbs. IEEE Spectrum reports that speeds on ATM networks are expected to reach 10 Gbps. Along with SONET and several other technologies, ATM is a key component of broadband ISDN (BISDN).
 
 

In the Integrated Services Digital Network (ISDN), the B-channel is the channel that carries the main data. (The "B" stands for "bearer" channel.)

In ISDN, there are two levels of service: the Basic Rate, intended for the home and small enterprise, and the Primary Rate, for larger users. Both rates include a number of B (bearer) channels and a D (delta) channel. The B channels carry data, voice, and other services. The D channel carries control and signaling information.

The Basic Rate consists of two 64 Kbps B channels and one 16 Kbps D channel. Thus, a Basic Rate user can have up to 128 Kbps service. The Primary Rate consists of 23 B channels and one 64 Kpbs D channel in the United States or 30 B channels and 1 D channel in Europe.

Pacific Bell, which offers ISDN to users in urban areas of California, provides an introduction to ISDN as part of their Web site.
 
 

A backbone is a larger transmission line that carries data gathered from smaller lines that interconnect with it.

1) At the local level, a backbone is a line or set of lines that local area networks connect to for a wide area network connection or within a local area network to span distances efficiently (for example, between buildings).

2) On the Internet or other wide area network, a backbone is a set of paths that local or regional networks connect to for long-distance interconnection. The connection points are known as network nodes or telecommunication data switching exchanges (DSEs).
 
 

A baseband is the original frequency range of a signal before it is modulated into a higher and more efficient frequency range, usually in multiplexing the signal to send it on a carrier with other signals at the same time.
 
 

BEDO DRAM (Burst Extended Data Output DRAM) is a type of dynamic random access memory (DRAM) that can send data back to the computer from one read operation at the same time it is reading in the address of the next data to be sent. In addition, after reading the address, it is able to send the data back in three successive clock cycles without clock coordination (that is, the three successive outputs seem to be sent from the RAM in a sudden burst). It works well with microprocessors that operate up to 66 MHz.
 
 

A BNC (Bayonet Neil-Concelman) connector is a type of connector used to connect a computer to a coaxial cable in a 10BASE-2 Ethernet network. 10BASE-2 is a 10 MHz baseband network on a cable extending up to 185 meters - the 2 is a rounding up to 200 meters - without a repeater cable. 10BASE-2 Ethernets are also known as "thinnets", "thin Ethernet", or "cheapernets". The wiring in this type of Ethernet is thin, 50 ohm, baseband coaxial cable. The BNC connector in particular is generally easier to install and less expensive than other coaxial connectors.

A BNC male connector has a pin that connects to the primary conducting wire and then is locked in place with an outer ring that turns into locked position.

Different sources offer different meanings for the letters BNC. However, our most knowledgable source indicates that the B stands for a bayonet-type connection (as in the way a bayonet attaches to a rifle) and the NC for the inventors of the connector, Neil and Concelman.
 
 

In telecommunications networks, a bridge is a product that connects a local area network (LAN) to another local area network that uses the same protocol (for example, Ethernet or Token Ring). You can envision a bridge as being a device that decides whether a message from you to someone else is going to the local area network in your building or to someone on the local area network in the building across the street. A bridge examines each message on a LAN, "passing" those known to be within the same LAN, and forwarding those known to be on the other interconnected LAN (or LANs).

In bridging networks, computer or node addresses have no specific relationship to location. For this reason, messages are sent out to every address on the network and accepted only by the intended destination node. Bridges learn which addresses are on which network and develop a learning table so that subsequent messages can be forwarded to the right network.

Bridging networks are generally always interconnected local area networks since broadcasting every message to all possible destinations would flood a larger network with unnecessary traffic. For this reason, routing networks such as the Internet use a scheme that assigns addresses to nodes so that a message or packet can be forwarded only in one general direction rather than forwarded in all directions.

A bridge works at the data-link (physical network) level of a network, copying a data frame from one network to the next network along the communications path.

A bridge is sometimes combined with a router in a product called a brouter.
 
 

Broadband refers to telecommunication that provides multiple channels of data over a single communications medium using frequency division multiplexing.
 
 

A bus master is the program, either in a microprocessor or more usually in a separate I/O controller, that directs traffic on the computer bus or input/output paths. The bus master is the "master" and the I/O devices on the bus are the "slaves." The bus master actually controls the bus paths on which the address and control signals flow. Once these are set up, the flow of data bits goes directly between the I/O device and the microprocessor.
 
 

Burst is a term used in a number of information technology contexts to mean a specific amount of data sent or received in one intermittent operation. It can be contrasted with streamed, paced, or continuous. Generally, a burst operation implies that some threshold has been reached that triggers the burst. Depending on the particular technology, a burst operation can be intermittent at a regular or an irregular rate.
 
 

A cache (pronounced CASH) is a place to store something more or less temporarily. Web pages you request are stored in your browser's cache directory on your hard disk. That way, when you return to a page you've recently looked at, the browser can get it from the cache rather than the original server, saving you time and the network the burden of some additional traffic. You can usually vary the size of your cache, depending on your particular browser.

Computers include caches at several levels of operation, including cache memory and a disk cache. Caching can also be implemented for Internet content by distributing it to multiple servers that are periodically refreshed. (The use of the term in this context is closely related to the general concept of a distributed information base.)

Altogether, we are aware of these types of caches:

• International, national, regional, organizational and other "macro" caches to which highly popular information can be distributed and periodically updated and from which most users would obtain information.
• Local server caches (for example, corporate LAN servers or access provider servers that cache frequently accessed files). This is similar to the previous idea, except that the decision of what data to cache may be entirely local.
• Your Web browser's cache, which contains the most recent Web files that you have downloaded and which is phyically located on your hard disk (and possibly some of the following caches at any moment in time)
• A disk cache (either a reserved area of RAM or a special hard disk cache) where a copy of the most recently accessed data and adjacent (most likely to be accessed) data is stored for fast access.
• RAM itself, which can be viewed as a cache for data that is initially loaded in from the hard disk (or other I/O storage systems).
• L2 cache memory, which is on a separate chip from the microprocessor but faster to access than regular RAM.
• L1 cache memory on the same chip as the microprocessor.

ANSI/EIA (American National Standards Institute/Eectronic Industries Association) Standard 568 is one of several standards that specify "categories" (the singular is commonly referred to as "CAT") of twisted pair cabling systems (wires, junctions, and connectors) in terms of the data rates that they can sustain. The specifications describe the cable material as well as the types of connectors and junction blocks to be used in order to conform to a category. These categories are:

The two most popular specifications are CAT 3 and CAT 5. While the two cables may look identical, CAT 3 is tested to a lower set of specifications and can cause transmission errors if pushed to faster speeds. CAT 3 cabling is NEXT-certified for only a 16 MHz signal, while CAT 5 cable must pass a 100 MHz test.
 
 

The Centronics parallelinterface is an older and still widely-used standard I/O interface for connecting printers and certain other devices to computers. The interface typically includes a somewhat cumbersome cable and a 36-pin male and female connector at the printer or other device. The cable plugs into a 25-pin parallel port on the computer. Data flows in one direction only, from the computer to the printer or other device. In addition to eight parallel data lines, other lines are used to read status information and send control signals. Centronics Corporation designed the original Centronics parallel interface for dot matrix printers. In 1981, IBM used this interface as an alternative to the slower one-bit-at-a-time serial interface.

When the Centronics parallel interface was first developed, the main peripheral was the printer. Since then, portable disk drives, tape backup drives, and CD-ROM players are among devices that have adopted the parallel interface. These new uses caused manufacturers to look at new ways to make the Centronics parallel interface better. In 1991, Lexmark, IBM, Texas instruments, and others met to discuss a standard that would offer more speed and bi-directional communication. Their effort and the sponsorship of the IEEE (Institute of Electrical and Electronics Engineers) resulted in the IEEE 1284 committee. The IEEE 1284 standard was approved for release in March, 1994.

The IEEE 1284 standard specifies five modes of operation, each mode providing data transfer in either the forward direction (computer to peripheral), backward direction (peripheral to computer), or bi-directional (one direction at a time).

• Compatibility mode is the original Centronics parallel interface and intended for use with dot matrix printers and older laser printers. The compatibility mode can be combined with the nibble mode for bi-directional data transfer.
• Nibble mode allows data transfer back to the computer. The nibble mode uses the status lines to send 2 nibbles (4-bit units) of data to the computer in two data transfer cycles. This mode is best used with printers.
• Byte mode uses software drivers to disable the drivers that control the data lines in order for data to be sent from the printer to the computer. The data is sent at the same speed as when data is sent from the computer to the printer. One byte of data is transferred instead of the two data cycles required by the nibble mode.
• ECP mode (Enhanced Capability Port mode) is an advanced bi-directional mode for use with printers and scanners. It allows data compression for images, FIFO (first in, first out) for items in queues, and high-speed, bi-directional communication. Data transfer occurs at two to four megabytes per second. An advanced feature of ECP is channel addressing. This is used for multifunction devices such as printer/fax/modem devices. For example, if a printer/fax/modem device needs to print and send data over the modem at the same time, the channel address software driver of the ECP mode assigns a new channel to the modem so that both devices can work simultaneously.
• EPP mode (Enhanced Parallel Port mode) was designed by Intel, Xircom, and Zenith Data Systems to provide a high-performance parallel interface that could also be used with the standard interface. EPP mode was adopted as part of the IEEE 1284 standard. The EPP mode uses data cycles that transfer data between the computer and the peripheral and address cycles that assign address, channel, or command information. This allows data transfer speeds of 500 kilobytes to 2 megabytes per second, depending on the speed of the slowest interface. The EPP mode is bi-directional. It is suited for network adapters, data acquisition, portable hard drives, and other devices that need speed.

A cookie is information that a Web site puts on your hard disk so that it can remember something about you at a later time. (More technically, it is information for future use that is stored by the server on the client side of a client/server communication.) Typically, a cookie records your preferences when using a particular site. Using the Web's Hypertext Transfer Protocol (HTTP), each request for a Web page is independent of all other requests. For this reason, the Web page server has no memory of what pages it has sent to a user previously or anything about your previous visits. A cookie is a mechanism that allows the server to store its own information about a user on the user's own computer. You can view the cookies that have been stored on your hard disk (although the content stored in each cookie may not make much sense to you). The location of the cookies depends on the browser. Internet Explorer stores each cookie as a separate file under a Windows subdirectory. Netscape stores all cookies in a single cookies.txt fle. Opera stores them in a single cookies.dat file.

Cookies are commonly used to rotate the banner ads that a site sends so that it doesn't keep sending the same ad as it sends you a succession of requested pages. They can also be used to customize pages for you based on your browser type or other information you may have provided the Web site. Web users must agree to let cookies be saved for them, but, in general, it helps Web sites to serve users better.
 
 

Dial-up pertains to a telephone connection in a system of many lines shared by many users. A dial-up connection is established and maintained for a limited time duration. The alternative is a dedicated connection, which is continuously in place. Dial-up lines are sometimes called switched lines and dedicated lines are called nonswitched lines. A dedicated line is often a leased line that is rented from a telephone company.

A dial-up connection can be initiated manually or automatically by your computer's modem or other device.
 
 

DirectX is an application program interface (API) for creating and managing graphic images and multimedia effects in applications such as games or active Web pages that will run in Microsoft's Windows 95 operating system. (Such an application program might be written in C++, or Visual C/C++, or Java.) The capability to "play" DirectX applications comes as an integrated part of Microsoft's Internet Explorer 4.0 Web browser. (A 3-D player is optionally downloadable.)

The DirectX Software Development Kit (SDK) includes tools that let a developer create or integrate graphic images, overlays, sprites, and other game elements, including sound. There is also a Driver Development Kit (DDK) that lets developers create drivers for display, audio, and other I/O devices.

DirectX is part of Microsoft's larger vision of an object-oriented development environment. For example, a sprite is created as an instance of a sprite class. Developers can also take advantage of Microsoft's set of prepackaged routines or small programs that are part of the Microsoft Foundation Class (MFC).

DirectX is designed so that some functions can be performed on a graphics accelerator card, freeing the microprocessor for other work. The accelerator manufacturer provides a driver especially for DirectX.

DirectX consists of five components:

• DirectDraw, an interface that lets you define two-dimensional images, specify textures, and manage double buffers (a technique for changing images)
• Direct3D, an interface for creating three-dimensional images
• DirectSound, an interface for integrating and coordinating sound with the images
• DirectPlay, a plug-in for end users, is also used by developers to test their application

DirectInput, an interface for input from I/O devicesDavid Joffe offers a Guide to Programming Games with DirectX.

Direct Memory Access is a capability provided by some computer bus architectures that allows data to be sent directly from an attached device (such as a disk drive) to the memory on the computer's motherboard. The microprocessor is freed from involvement with the data transfer, thus speeding up overall computer operation.

Usually a specified portion of memory is designated as an area to be used for direct memory access. In the ISA bus standard, up to 16 megabytes of memory can be addressed for DMA. The EISA and MCA standards allow access to the full range of memory addresses (assuming they're addressable with 32 bits). PCI accomplishes DMA by using bus mastering (with the microprocessor "delegating" I/O control to the PCI controller).

The domain name system (DNS) is the way that Internet domain names are located and translated into IP (Internet Protocol) addresses. A domain name is a meaningful and easy-to-remember "handle" for an Internet address.

Because maintaining a central list of domain name/IP address correspondences would be impractical, the lists of domain names and IP addresses are distributed throughout the Internet in a hierarchy of authority. There is probably a DNS server within close geographic proximity to your access provider that maps the domain names in your Internet requests or forwards them to other servers in the Internet.
 
 

In computers, a dynamic link library (DLL) is a collection of small programs, any of which can be called when needed by a larger program that is running in the computer. The small program that lets the larger program communicate with a specific device such as a printer or scanner is often packaged as a DLL program (usually referred to as a DLL file).

The advantage of DLL files is that, because they don't get loaded into random access memory (RAM) together with the main program, space is saved in RAM. When and if a DLL file is needed, then it is loaded and run. For example, as long as a user of Microsoft Word is editing a document, the printer DLL file does not need to be loaded into RAM. If the user decides to print the document, then the Word application causes the printer DLL file to be loaded and run.

A DLL file is often given a ".dll" file name suffix. DLL files are dynamically linked with the program that uses them during program execution rather than being compiled with the main program. The set of such files (or the DLL) is somewhat comparable to the library routines provided with programming languages such as C and C++.
 
 

Direct Memory Access is a capability provided by some computer bus architectures that allows data to be sent directly from an attached device (such as a disk drive) to the memory on the computer's motherboard. The microprocessor is freed from involvement with the data transfer, thus speeding up overall computer operation.

Usually a specified portion of memory is designated as an area to be used for direct memory access. In the ISA bus standard, up to 16 megabytes of memory can be addressed for DMA. The EISA and MCA standards allow access to the full range of memory addresses (assuming they're addressable with 32 bits). PCI accomplishes DMA by using bus mastering (with the microprocessor "delegating" I/O control to the PCI controller).

An alternative to DMA is the Programmed Input/Output (PIO) interface in which all data transmitted between devices goes through the processor. A newer protocol for the ATA/IDE interface is Ultra DMA/33, which provides a burst data transfer rate up to 33 MB (megabytes) per second. Hard drives that come with Ultra DMA/33 also support PIO modes 1, 3, and 4, and multiword DMA mode 2 (at 16.6 megabytes per second).
 
 

In general, a domain is an area of control or a sphere of knowledge.

In computing and telecommunication in general, a domain is a sphere of knowledge identified by a name. Typically, the knowledge is a collection of facts about some program entities or a number of network points or addresses.

On the Internet, a domain consists of a set of network addresses. This domain is organized in levels. The top level identifies geographic or purpose commonality (for example, the nation that the domain covers or a category such as "commercial"). The second level identifies a unique place within the top level domain and is, in fact, equivalent to a unique address on the Internet (or IP). Lower levels of domain may also be used.

Strictly speaking, in the Internet's domain name system (DNS), a domain is a name with which name server records are associated that describe subdomains or hosts. For example, "abc.com" could be a domain with records for "www.abc.com" and "www1.abc.com," and so forth.
 
 

The dot pitch specification for a display monitor tells you how sharp the displayed image can be. The dot pitch is measured in millimeters (mm) and a smaller number means a sharper image. In desk top monitors, common dot pitches are .31mm, .28mm, .27mm, .26mm, and .25mm. Personal computer users will usually want a .28mm or finer. Some large monitors for presentation use may have a larger dot pitch (.48mm, for example). Think of the dot specified by the dot pitch as the smallest physical visual component on the display. A pixel is the smallest programmable visual element and maps to the dot if the display is set to its highest resolution. When set to lower resolutions, a pixel encompasses multiple dots.

Technically, in a cathode ray tube (CRT) display with a shadow mask, the dot pitch is the distance between the holes in the shadow mask, measured in millimeters (mm). The shadow mask is a metal screen filled with holes through which the three electron beams pass that focus to a single point on the tube's phosphor surface. In CRTs that use an aperture grill (a slotted form of mask), such as Sony's Trinitron flat-screen technology, the dot pitch is the difference between adjacent slots that pass through an electron beam of the same color.
 
 

DOS memory, sometimes referred to as conventional memory, refers to the memory-addressing scheme used in the original IBM and compatible PCs. These came with only one operating system, DOS, and this operating system had to be designed to work with the PC's microprocessor, the Intel 8088. Because of 8088 engineering limitations, storage or memory addresses were limited to a maximum of one megabyte. (Later, of course, PC's came with 2, 4, 8, and today's common 16 and 32 megabytes of RAM.) At the time, however, one megabyte was considered a rather large amount of memory to be able to access.

A certain amount of the random access memory was reserved as a place to load in the BIOS or initializing program, another space was reserved for buffer areas for display data, and another space for interrupt data, and so forth. The remaining 640 kilobytes of memory could be used by the DOS operating system (which was relatively small) and application programs.

The reason that all of this is not academic is that, as new microprocessors and operating systems have been developed, many older programs written with the original memory addressing limitations need to continue running in the newer systems. This means that the newer systems have had to accommodate the older programs so that they can run in the original limited 640 kilobye contiguous address range. A program that is run with this constraint is described as running in real mode. (Programs running without this constraint are described as running in protected mode.)

With the successors to the 8088, the 80286 and 80386 microprocessors, available memory increased considerably, with up to 15 megabytes possible in a 286 and up to almost 4 gigabytes of RAM possible in a 386. This extra memory above the orginal one megabyte that DOS was designed to address is called extended memory. Being able to address extended memory means running in protected mode.

In general, DOS applications can only run in real mode since DOS itself requires the memory constraint. However, some programs have been developed called DOS extenders that can be compiled with the application and provide a built-in memory management capability. In order for multiple DOS programs with memory extenders to run concurrently, some common approach was required so that programs could share the extended memory effectively. Several standards developed to manage this sharing: XMS (Extended Memory Specification), VCPI (Virtual Control Program Interface), and DPMI (DOS protected mode interface).
 
 

1) In computers, dots per inch (dpi) is a measure of the sharpness (that is, the density of illuminated points) on a display screen. The dot pitch determines the absolute limit of the possible dots per inch. However, the displayed resolution of pixels (picture elements) that is set up for the display is usually not as fine as the dot pitch. The dots per inch for a given picture resolution will differ based on the overall screen size since the same number of pixels are being spread out over a different space. Some users prefer the term "pixels per inch (ppi)" as a measure of display image sharpness, reserving dpi for use with the print medium.

2) In printing, dots per inch (dpi) is the usual measure of printed image quality on the paper. The average personal computer printer today provides 300 dpi or 600 dpi. Choosing the higher print quality usually reduces the speed of printing each page.
 
 

DVD (digital versatile disk) is an optical disk technology that is expected to rapidly replace the CD-ROM disk (as well as the audio compact disc) over the next few years. The digital versatile disk (DVD) holds 4.7 gigabytes of information on one of its two sides, or enough for a 133-minute movie. With two layers on each of its two sides, it will hold up to 17 gigabytes of video, audio, or other information. (Compare this to the current CD-ROM disk of the same physical size, holding 600 megabytes. The DVD can hold more than 28 times as much information!)

DVD-Video is the usual name for the DVD format designed for full-length movies and is a box that will work with your television set. DVD-ROM is the name of the player that will (sooner or later) replace your computer's CD-ROM. It will play regular CD-ROM disks as well as DVD-ROM disks. DVD-RAM is the writeable version. DVD-Audio is a player designed to replace your compact disc player.

DVD uses the MPEG-2 file and compression standard. MPEG-2 images have four times the resolution of MPEG-1 images and can be delivered at 60 interlaced fields per second where two fields constitute one image frame. (MPEG-1 can deliver 30 noninterlaced frames per second.) Audio quality on DVD is comparable to that of current audio compact disks.
 
 

E-commerce (electronic commerce or EC) is the buying and selling of goods and services on the Internet, especially the World Wide Web. In practice, this term and a new term, "e-business," are often used interchangably. For online retail selling, the term e-tailing is sometimes used.

E-commerce can be divided into:

E-tailing or "virtual storefronts" on Web sites with online catalogs, sometimes gathered into a "virtual mall"

The gathering and use of demographic data through Web contacts

Electronic Data Interchange (EDI), the business-to-business exchange of data

E-mail and fax and their use as media for reaching prospects and established customers (for example, with newsletters)

Business-to-business buying and selling

The security of business transactions
 
 

E-tailing or The Virtual Storefront and the Virtual Mall

As a place for direct retail shopping, with its 24-hour availability, a global reach, the ability to interact and provide custom information and ordering, and multimedia prospects, the Web is rapidly becoming a multibillion dollar source of revenue for the world's businesses. A number of businesses already report considerable success. As early as the middle of 1997, Dell Computers reported orders of a million dollars a day. By early 1999, projected e-commerce revenues for business were in the billions and the stocks of companies deemed most adept at e-commerce were skyrocketing. Apart from computer and network products, books (Amazon.com), gardening products (Garden.com), music on compact disks (CDNow), and office supplies (SuppliesOnline) were a few of the better-known e-commerce sites. By early 1999, even businesses that have always counted on face-to-face customer interaction were planning e-commerce Web sites and many businesses were planning how to coordinate in-store and Web store retail approaches. Meanwhile, new businesses based entirely on Web sales were being invented daily.

Market Research

In early 1999, it was widely recognized that because of the interactive nature of the Internet, companies could gather data about prospects and customers in unprecedented amounts -through site registration, questionnaires, and as part of taking orders. The issue of whether data was being collected with the knowledge and permission of market subjects had been raised. (Microsoft referred to its policy of data collection as "profiling" and a proposed standard has been developed that allows Internet users to decide who can have what personal information.)

Electronic Data Interchange (EDI)

EDI is the exchange of business data using an understood data format. It predates today's Internet. EDI involves data exchange among parties that know each other well and make arrangements for one-to-one (or point-to-point) connection, usually dial-up.

E-Mail, Fax, and Internet Telephony

E-commerce is also conducted through the more limited electronic forms of communication called e-mail, facsimile or fax, and the emerging use of telephone calls over the Internet. Most of this is business-to-business, with some companies attempting to use e-mail and fax for unsolicited ads (usually viewed as online junk mail or spam) to consumers and other business prospects. An increasing number of business Web sites offer e-mail newsletters for subscribers. A new trend is opt-in e-mail in which Web users voluntarily sign up to receive e-mail, usually sponsored or containing ads, about product categories or other subjects they are interested in.

Business-to-Business Buying and Selling

Thousands of companies that sell products to other companies have discovered that the Web provides not only a 24-hour-a-day showcase for their products but a quick way to reach the right people in a company for more information.

The Security of Business Transactions

Security includes authenticating business transactors, controlling access to resources such as Web pages for registered or selected users, encrypting communications, and, in general, ensuring the privacy and effectiveness of transactions. Among the most widely-used security technologies are SSL and RSA. Secure Electronic Transactions (SET) is an emerging industry standard.
 
 

EISA is a standard bus (computer interconnection) architecture that extends the ISA standard to a 32-bit interface. It was developed in part as an open alternative to the proprietary Micro Channel Architecture (MCA) that IBM introduced in its PS/2 computers. EISA data transfer can reach a peak of 33 megabytes per second.
 
 

EPP/ECP (Enhanced Parallel Port/Enhanced Capability Port) is a standard signaling method for bi-directional parallel communication between a computer and peripheral devices that offers the potential for much higher rates of data transfer than the original parallel signaling methods. EPP is for non-printer peripherals. ECP is for printers and scanners. EPP/ECP are part of IEEE Standard 1284, which also specifies support for current signaling methods (including Centronics, the de facto standard for printer communication) so that both old and new peripherals can be accommodated.

The new standard specifies five modes of data transfer. Three of them support the older mono-directional modes (a forward direction method from PC to Centronics printer and two reverse direction methods from peripheral to the PC). The fourth and fifth modes, EPP and ECP, are bi-directional (half-duplex) signaling methods, meaning that they are designed for back-and-forth communication. Partly because these are being implemented in hardware, EPP and ECP will provide much faster data transfer. The first three methods offer an effective data transfer rate of 50 to 100 kilobytes per second. EPP and ECP offer the possibility of rates "in excess of 1 megabytes per second," according to Warp Nine, a chip manufacturer.

In order to get the maximum advantage of EPP/ECP, both operating system (or an I/O port controller, or both) and peripheral device must support the standard. Initially, you may get the best effect from EPP and a Zip drive. Even printers that support ECP are limited by the mechanical aspects of printing. Nevertheless, even users of the compatibility modes of Standard 1284 are also expected to see some benefit in data transfer to and from peripherals.

Currently, Windows 95 has built-in support for IEEE 1284 in its parallel plug-and-play feature. It also supports ECP in forward direction, assuming you have a printer and a parallel port with ECP. IBM is planning to add 1284 support to its OS/2 operating system. It is likely that other vendors will provide ECP or EPP software for other operating systems.
 
 

Extended data output (EDO) RAM is a type of random access memory (RAM) chip that improves the time to read from memory on faster microprocessors such as the Intel Pentium. EDO RAM was initially optimized for the 66 MHz Pentium. For faster computers, different types of synchronous dynamic RAM (SDRAM) are recommended.
 
 

E1 (or E-1) is a European digital transmission format devised by the ITU-T and given the name by the Conference of European Postal and Telecommunication Administration (CEPT). It's the equivalent of the North American T-1 format. E2 through E5 are carriers in increasing multiples of the E1 format.

The E1 signal format carries data at a rate of 2.048 million bits per second and can carry 32 channels of 64 Kbps* each. E1 carries at a somewhat higher data rate than T-1 (which carries 1.544 million bits per second) because, unlike T-1, it does not do bit-robbing and all eight bits per channel are used to code the signal. E1 and T-1 can be interconnected for international use.

E2 (E-2) is a line that carries four multiplexed E1 signals with a data rate of 8.448 million bits per second.

E3 (E-3) carries 16 E1 signals with a data rate of 34.368 million bits per second.

E4 (E-4) carries four E3 channels with a data rate of 139.264 million bits per second.

E5 (E-5) carries four E4 channels with a data rate of 565.148 million bits per second.

• In international English outside the U.S., the equivalent usage is "kbps" or "kbits s^-1."

 

 
 
 

Ethernet is the most widely-installed local area network technology. Now specified in a standard, IEEE 802.3, Ethernet was originally developed by Xerox and then developed further by Xerox, DEC, and Intel. An Ethernet LAN typically uses coaxial cable or special grades of twisted pair wires. The most commonly installed Ethernet systems are called 10BASE-T and provide transmission speeds up to 10 Mbps. Devices are connected to the cable and compete for access using a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol.

Fast Ethernet is a local area network (LAN) transmission standard that provides a data rate of 100 megabits per second (referred to as "100BASE-T10"). Workstations with existing 10 megabit per second (10BASE-T) Ethernet cards can be connected to a Fast Ethernet network. (The 100 megabits per second is a shared data rate; input to each workstation would be constrained by the 10 Mbps card.)
 
 

Prior to newer forms of DRAM, Fast Page Mode DRAM (FPM DRAM) was the most common kind of dynamic random access memory (DRAM) in personal computers. Page mode DRAM essentially accesses a row of RAM without having to continually respecify the row. A row access strobe (RAS) signal is kept active while the column access strobe (CAS) signal changes to read a sequence of contiguous memory cells. This reduces access time and lowers power requirements. Clock timings for FPM DRAM are typically 6-3-3-3 (meaning 3 clock cycles for access setup, and 3 clock cycles for the first and each of three successive accesses based on the initial setup).
 
 

A file allocation table (FAT) is a table that an operating system maintains on a hard disk that provides a map of the clusters (the basic unit of logical storage on a hard disk) that a file has been stored in. When you write a new file to a hard disk, the file is stored in one or more clusters that are not necessarily next to each other; they may be rather widely scattered over the disk. A typical cluster size is 2,048 bytes, 4,096 bytes, or 8,192 bytes. The operating system creates a FAT entry for the new file that records where each cluster is located and their sequential order. When you read a file, the operating system reassembles the file from clusters and places it as an entire file where you want to read it. For example, if this is a long Web page, it may very well be stored on more than one cluster on your hard disk.

Until Windows 95 OSR2 (OEM Release 2), DOS and Windows file allocation table entries were 16 bits in length, limiting hard disk size to 128 megabytes, assuming a 2,048 size cluster. Up to 512 megabyte support is possible assuming a cluster size of 8,192 but at the cost of using clusters inefficiently. DOS 5.0 and later versions provide for support of hard disks up to two gigabytes with the 16-bit FAT entry limit by supporting separate FATs for up to four partitions.

With 32-bit FAT entry (FAT32) support in Windows 95 OSR2, the largest size hard disk that can be supported is two terabytes! However, personal computer users are more likely to take advantage of FAT32 with 5 or 10 gigabyte drives.
 
 

Fiber optic (or "optical fiber") refers to the medium and the technology associated with the transmission of information as light impulses along a glass or plastic wire or fiber. Fiber optic wire carries much more information than conventional copper wire and is far less subject to electromagnetic interference. Most telephone company long-distance lines are now fiber optic.

Transmission on fiber optic wire requires repeating at distance intervals. The glass fiber requires more protection within an outer cable than copper. For these reasons and because the installation of any new wiring is labor-intensive, few communities yet have fiber optic wires or cables from the phone company's branch office to local customers (known as local loop).
 
 

Fibre Channel is a technology for transmitting data between computer devices at a data rate of up to 1 Gbps (one billion bits per second). (A data rate of 4 Gbps is proposed.) Fibre Channel is especially suited for connecting computer servers to shared storage devices and for interconnecting storage controllers and drives. Since it is three times as fast, Fibre Channel is expected to replace the Small System Computer Interface (SCSI) as the transmission interface between servers and clustered storage devices. It is also more flexible; devices can be as far as ten kilometers (about six miles) apart. The longer distance requires optical fiber as the physical medium. However, Fibre Channel also works using coaxial cable and ordinary telephone twisted pair.

Fibre Channel offers point-to-point, switched, and loop interfaces and interoperates with SCSI, the Internet Protocol (IP), and other protocols.

Manufacturers and early customers plan to use Fibre Channel to interconnect a number of servers with a common pool of storage devices (possibly including redundant arrays of independent disks (RAID). Vendors that offer or plan to offer Fibre Channel storage devices, switches, hubs, and subsystems include Compaq, Data General, Dell, EMC, IBM, Storage Technologies, StorageTek, and Sun Microsystems.

Fibre Channel is specified by a set of standards, but mainly the Fibre Channel Physical and Signalling standard, ANSI X3.230-1994, which is also ISO 14165-1.
 
 

FireWire is Apple Computer's version of a new standard, IEEE 1394 High Performance Serial Bus, for connecting devices to your personal computer. FireWire provides a single plug-and-socket connection on which up to 63 devices can be attached with data transfer speeds up to 400 Mbps (megabits per second). The standard describes a serial bus or pathway between one or more peripheral devices and your computer's microprocessor. In the next few years, you can expect to see many peripheral devices coming equipped to meet this new standard. FireWire and other IEEE 1394 implementations provide:

• A simple common plug-in serial connector on the back of your computer and on many different types of peripheral devices
• A thin serial cable rather than the thicker parallel cable you now use to your printer, for example
• A very high-speed rate of data transfer that will accommodate multimedia applications (100 and 200 megabits per second today; with much higher rates later)
• Hot-plug and plug-and-play capability without disrupting your computer
• The ability to chain devices together in a number of different ways without terminators or complicated set-up requirements

Briefly How It Works

There are two levels of interface in IEEE 1394, one for the backplane bus within the computer and another for the point-to-point interface between device and computer on the serial cable. A simple bridge connects the two environments. The backplane bus supports 12.5, 25, or 50 megabits per second data transfer. The cable interface supports 100, 200, or 400 megabits per second. Each of these interfaces can handle any of the possible data rates and change from one to another as needed.

The serial bus functions as though devices were in slots within the computer sharing a common memory space. A 64-bit device address allows a great deal of flexibility in configuring devices in chains and trees from a single socket.

IEEE 1394 provides two types of data transfer: asynchronous and isochronous. Asynchronous is for traditional load-and-store applications where data transfer can be initiated and an application interrupted as a given length of data arrives in a buffer. Isochronous data transfer ensures that data flows at a pre-set rate so that an application can handle it in a timed way. For multimedia applications, this kind of data transfer reduces the need for buffering and helps ensure a continuous presentation for the viewer.

The 1394 standard requires that a device be within 4.5 meters of the bus socket. Up to 16 devices can be connected in a single chain, each with the 4.5 meter maximum (before signal attenuation begins to occur) so theoretically you could have a device as far away as 72 meters from the computer.

Another new approach to connecting devices, the Universal Serial Bus (USB), provides the same "hot plug" capability as the 1394 standard. It's a less expensive technology but data transfer is limited to 12 Mbps (million bits per second). SCSI offers a high data transfer rate (up to 40 megabytes per second) but requires address preassignment and a device terminator on the last device in a chain. FireWire can work with the latest internal computer bus standard, PCI, but higher data transfer rates may require special design considerations to minimize undesired buffering for transfer rate mismatches.
 
 

Frame relay is based on the older X.25 packet-switching technology which was designed for transmitting analog data such as voice conversations. Unlike X.25 which was designed for analog signals, frame relay is a fast-packet technology, which means that the protocol does not attempt to correct errors. When an error is detected in a frame, it is simply "dropped." (thrown away). The end points are responsible for detecting and retransmitting dropped frames. (However, the incidence of error in digital networks is extraordinarily small relative to analog networks.)

Frame relay is often used to connect local area networks with major backbones as well as on public wide area networks and also in private network environments with leased lines over T-1 lines. . It requires a dedicated connection during the transmission period. It's not ideally suited for voice or video transmission, which requires a steady flow of transmissions. However, under certain circumstances, it is used for voice and video transmission.

Frame relay relays packets at the data-link layer of the Open Systems Interconnection (OSI) model rather than at the network layer. A frame can incorporate packets from different protocols such as Ethernet and X.25. It is variable in size and can be as large as a thousand bytes or more.
 
 

A gateway is a network point that acts as an entrance to another network. On the Internet, in terms of routing, the network consists of gateway nodes and host nodes. The computers of network users and the computers that serve content (such as Web pages) are host nodes. The computers that control traffic within your company's network or at your local Internet service provider (ISP) are gateway nodes.

In the network for an enterprise, a computer server acting as a gateway node is often also acting as a proxy server and a firewall server. Gateways also involve the use of routers and switches.
 
 

Gigabit Ethernet is a local area network (LAN) transmission standard that provides a data rate of 1 billion bits per second (one gigabit). Gigabit Ethernet is defined in the IEEE 802.3 standard and the first product versions of it are now available. Gigabit Ethernet is used as an enterprisebackbone.

Gigabit Ethernet is carried primarily on optical fiber (with very short distances possible on copper media). Existing Ethernet LANs with 10 and 100 Mbps cards can feed into a Gigabit Ethernet backbone. An alternative technology that competes with Gigabit Ethernet is ATM.
 
 

GSM (Global System for Mobile communication) is a digital mobile telephone system that is widely used in Europe and other parts of the world. GSM uses a variation of time division multiple access (TDMA) and is the most widely used of the three digital wireless telephone technologies (TDMA, GSM, and CDMA). GSM digitizes and compresses data, then sends it down a channel with two other streams of user data, each in its own time slot. It operates at either the 900 MHz or 1800 MHz frequency band.

GSM is the de facto wireless telephone standard in Europe. GSM has over 120 million users worldwide and is available in 120 countries, according to the GSM MoU Association. Since many GSM network operators have roaming agreements with foreign operators, users can often continue to use their mobile phones when they travel to other countries.

American Personal Communications (APC), a subsidiary of Sprint, is using GSM as the technology for a broadband personal communications service (PCS). The service will ultimately have more than 400 base stations for the palm-sized handsets that are being made by Ericsson, Motorola, and Nokia. The handsets include a phone, a text pager, and an answering machine.

GSM together with other technologies is part of an evolution of wireless mobile telemmunication that includes High-Speed Circuit-Switched Data (HSCSD), General Packet Radio System (GPRS), Enhanced Data GSM Environment (EDGE), and Universal Mobile Telecommunications Service (UMTS).
 
 

HSSI (High-Speed Serial Interface) is a short-distance communications interface that is commonly used to interconnect routing and switching devices on local area networks (LANs) with the higher-speed lines of a wide area network (WAN). HSSI is used between devices that are within fifty feet of each other and achieves data rates up to 52 Mbps. Typically, HSSI is used to connect a LANrouter to a T3 line. HSSI can be used to interconnect devices on token ring and Ethernet LANs with devices that operate at Synchronous Optical Network (SONET) OC-1 (Optical Carrier 1) speeds or on T3 lines. HSSI is also used for host-to-host linking, image processing, and disaster recovery applications.

Like ISDN and ADSL, HSSI operates at the physical layer of a network, using the standard Open Systems Interconnection (OSI) model. The electrical connection uses a 50-pin connector. The HSSI transmission technology uses differential emitter-coupled logic (ECL). HSSI uses gapped timing. Gapped timing allows a Data Communications Equipment (DCE) device to control the flow of data being transmitted from a Data Terminating Equipment (DTE) device such as a terminal or computer by adjusting the clock speed or deleting clock impulses.

For diagnosing problems, HSSI offers four loopback tests. The first loopback tests the cable by looping the signal back after it reaches the DTE port. The second and third loopbacks test the line ports of the local DCE and the remote DTE. The fourth tests the DTE's DCE port. HSSI requires two control signals ("DTE available" and "DCE available") before the data circuit is valid.

The HSSI cable uses the same number of pins and wires as a SCSI-2 (Small Computer Systems Interface 2) cable, but uses the HSSI electrical interface. It is not recommended to use a SCSI-2 cable with an HSSI interface.
 
 

In general, a hub is the central part of a wheel where the spokes come together. The term is familiar to frequent fliers who travel through airport "hubs" to make connecting flights from one point to another. In data communications, a hub is a place of convergence where data arrives from one or more directions and is forwarded out in one or more other directions. A hub usually includes a switch of some kind. (And a product that is called a "switch" could usually be considered a hub as well.) The distinction seems to be that the hub is the place where data comes together and the switch is what determines how and where data is forwarded from the place where data comes together. Regarded in its switching aspects, a hub can also include a router.

1) In describing network topologies, a hub topology consists of a backbone (main circuit) to which a number of outgoing lines can be attached ("dropped"), each providing one or more connection ports for devices to attach to. For Internet users not connected to a local area network, this is the general topology used by your access provider. Other common network topologies are the bus network and the ring network. (Either of these could possibly feed into a hub network, using a bridge.)

2) As a network product, a hub may include a group of modem cards for dial-in users, a gateway card for connections to a local area network (for example, an Ethernet or a Token Ring), and a connection to a T-1 line (the main line in this example).
 
 

An i-net (pronounced AI-neht) is any network that uses the Internet Protocol (IP). Within AT&T, the word is used as a convenient "umbrella" term that includes the Internet, intranets, and extranets.
 
 

An interlaced display is a cathode-ray tube (CRT) display in which the lines are scanned alternately in two interwoven rasters.

In a CRT display, there are several hundred horizontal lines in a frame (full screen). These lines are scanned from left to right, and from top to bottom. The refresh rate (number of frames scanned per second) varies, but it is normally between 60 and 100 Hz. Refresh rates slower than 60 Hz produce distracting screen flicker, which can cause headaches and eye fatigue.

Most CRT computer monitors scan each line in turn from top to bottom at the lowest resolution levels (640 x 480 and 800 x 600 pixels). However, at the higher resolutions, such as 1024 x 768 or 1200 x 800, the frame is sometimes scanned in interlaced fashion: first the odd-numbered lines, and then the even-numbered lines. This allows for a lower refresh rate without producing flicker. With text and fixed graphics displays, this scheme can work well. However, with animated graphics -- especially images that move or change form rapidly -- interlacing can produce a fluttering effect at least as irritating as screen flicker.

For serious animated-graphics work and video editing, a non- interlaced CRT display is recommended. The refresh rate should be as high as the system will allow, ideally 70 Hz or more.
 
 

Internet2 is a collaboration among more than 100 U.S. universities to develop networking and advanced applications for learning and research. Since much teaching, learning, and collaborative research may require real-time multimedia and high-bandwidth interconnection, a major aspect of Internet2 is adding sufficient network infrastructure to support such applications. But Internet2 also intends to investigate and develop new ways to use the Internet and the Internet2 infrastructure for its educational purposes. Although Internet2 is not envisioned as a future replacement for the Internet, its organizers hope to share their developments with other networks, including the Internet. Internet2 will include and further develop the National Science Foundation's very high-speed Backbone Network Service (vBNS) that currently interconnects research supercomputers in the U.S. The involved institutions plan to continue using the existing Internet for "ordinary" services such as e-mail, personal Web access, and newsgroups.

Internet2 collaborators plan to use Quality-of-Service (QoS) tools so that participants can reserve and use bandwidth for special events or in certain time periods. Here are some possibilities envisioned by Internet2:

Distributed learning modules: Conceptually, teachers and students can be share materials in cyberspace with students learning in a self-directed manner under the supervision of an educational system or teacher. Internet2 foresees tools that would make it easy to create what they call LearningWare, using existing object-oriented programming methodologies. Internet2 may also help realize the Instructional Management System (IMS), a standard process for using the Internet in developing and delivering learning packages and tracking outcomes. One can think of the IMS as a more structured way to exploit the potential learning materials on the World Wide Web.

New ways to envision and retrieve information: In the future, today's text-oriented models of information structure could be replaced by interactive pictures of information structure (compare a textual taxonomy or table of contents with illustrations of interlinked and explodable animal forms, for example). With Internet2's high-bandwidth connections, experiments in such information visualization will be possible; new ideas can be tried out. In environments where up-to-date information is valuable, information can be pushed to users at their request.

Virtual environment sharing: Sometimes called tele-immersion, participants in teleconferences could share the perception that everyone was in the same physical place, possibly with virtual (but somewhat real) models of shared work objects such as architectural models or multimedia storyboards. You would be able to see yourself with others in a far-away conference room, talking and perhaps manipulating objects in the room.

Virtual laboratory: A virtual laboratory would allow scientists in a number of different physical locations, each with unique expertise, computing resources, and/or data to collaborate efficiently not simply at a meeting but in an ongoing way. Effectively, such a project would extend and pool resources while engendering orderly communication and progress toward shared goals. For example, a group of astronomers and computer scientists at the supercomputing centers in the U.S. are attempting to share experiments and knowledge about the origin of the universe. Shared visualizations of alternative possibilities could conceivably suggest additional or refined alternatives. Virtual laboratories are also envisioned for the design and manufacturing of complex systems such as airplanes and for studying and forecasting weather patterns.
 
 

This definition is based on Internet Protocol Version 4. See Internet Protocol Version 6 (IPv6) for a description of the newer 128-bit IP address. Note that the system of IP address classes described here, while forming the basis for IP address assignment, is generally bypassed today by use of Classless Inter-Domain Routing (CIDR) addressing.

In the most widely installed level of the Internet Protocol (IP) today, an IP address is a 32-bit number that identifies each sender or receiver of information that is sent in packets across the Internet. When you request an HTML page or send e-mail, the Internet Protocol part of TCP/IP includes your IP address in the message (actually, in each of the packets if more than one is required) and sends it to the IP address that is obtained by looking up the domain name in the URL you requested or in the e-mail address you're sending a note to. At the other end, the recipient can see the IP address of the Web page requestor or the e-mail sender and can respond by sending another message using the IP address it received.

An IP address has two parts: the identifier of a particular network on the Internet and an identifier of the particular device (which can be a server or a workstation) within that network. On the Internet itself - that is, between the routers that move packets from one point to another along the route - only the network part of the address is looked at.
 
 

The IRQ (interrupt request) value is an assigned location where the computer can expect a particular device to interrupt it when the device sends the computer signals about its operation. For example, when a printer has finished printing, it sends an interrupt signal to the computer. The signal momentarily interrupts the computer so that it can decide what processing to do next. Since multiple signals to the computer on the same interrupt line might not be understood by the computer, a unique value must be specified for each device and its path to the computer. Prior to Plug-and Play (PnP) devices, users often had to set IRQ (interrupt request) values manually (or be aware of them) when adding a new device to a computer.

If you add a device that does not support Pnp, the manufacturer will hopefully provide explicit directions on how to assign IRQ values for it. If you don't know what IRQ value to specify, you'll probably save time by calling the technical support phone number for the device manufacturer and asking.
 
 

ISA is a standard bus (computer interconnection) architecture that is associated with the IBM AT motherboard. It allows 16 bits at a time to flow between the motherboard circuitry and an expansion slot card and its associated device(s).
 
 

An ISP (Internet service provider) is a company that provides individuals and other companies access to the Internet and other related services such as Web site building and hosting. An ISP has the equipment and the telecommunication line access required to have points-of-presence on the Internet for the geographic area served. The larger ISPs have their own high-speed leased lines so that they are less dependent on the telecommunication providers and can provide better service to their customers. Among the largest national and regional ISPs are AT&T WorldNet, IBM Global Network, MCI, Netcom, UUNet, and PSINet.

ISPs also include regional providers such as New England's NEARNet and the San Francisco Bay area BARNet. They also include thousands of local providers. In addition, Internet users can also get access through online service providers (OSPs) such as America Online and Compuserve.

The larger ISPs interconnect with each other through MAEs (ISP switching centers run by MCI WorldCom) or similar centers. The arrangements they make to exchange traffic are known as peering agreements. There are several very comprehensive lists of ISPs world-wide available on the Web.

An ISP is also sometimes referred to as an IAP (Internet access provider). ISP is sometimes used as an abbreviation for independent service provider to distinguish a service provider that is an independent, separate company from a telephone company.