RAID (redundant array of independent disks) is a way of storing the same data in different places (thus, redundantly) on multiple hard disks. By placing data on multiple disks, I/O operations can overlap in a balanced way, improving performance. Since multiple disks increases the mean time between failure (MTBF), storing data redundantly increases fault-tolerance.

A RAID appears to the operating system to be a single logical hard disk. RAID employs the technique of striping, which involves partitioning each drive's storage space into units ranging from a sector (512 bytes) up to several megabytes. The stripes of all the disks are interleaved and addressed in order.

In a single-user system where large records, such as medical or other scientific images, are stored, the stripes are typically set up to be small (perhaps 512 bytes) so that a single record spans all disks and can be accessed quickly by reading all disks at the same time.

In a multi-user system, better performance requires establishing a stripe wide enough to hold the typical or maximum size record. This allows overlapped disk I/O across drives.

There are at least nine types of RAID plus a non-redundant array (RAID-0):

• RAID-0. This technique has striping but no redundancy of data. It offers the best performance but no fault-tolerance.
• RAID-1. This type is also known as disk mirroring and consists of at least two drives that duplicate the storage of data. There is no striping. Read performance is improved since either disk can be read at the same time. Write performance is the same as for single disk storage. RAID-1 provides the best performance and the best fault-tolerance in a multi-user system.
• RAID-2. This type uses striping across disks with some disks storing error checking and correcting (ECC) information. It has no advantage over RAID-3.
• RAID-3. This type uses striping and dedicates one drive to storing parity information. The embedded error checking (ECC) information is used to detect errors. Data recovery is accomplished by calculating the exclusive OR (XOR) of the information recorded on the other drives. Since an I/O operation addresses all drives at the same time, RAID-3 cannot overlap I/O. For this reason, RAID-3 is best for single-user systems with long record applications.
• RAID-4. This type uses large stripes, which means you can read records from any single drive. This allows you to take advantage of overlapped I/O for read operations. Since all write operations have to update the parity drive, no I/O overlapping is possible. RAID-4 offers no advantage over RAID-5.
• RAID-5. This type includes a rotating parity array, thus addressing the write limitation in RAID-4. Thus, all read and write operations can be overlapped. RAID-5 stores parity information but not redundant data (but parity information can be used to reconstruct data). RAID-5 requires at least three and usually five disks for the array. It's best for multi-user systems in which performance is not critical or which do few write operations.
• RAID-6. This type is similar to RAID-5 but includes a second parity scheme that is distributed across different drives and thus offers extremely high fault- and drive-failure tolerance. There are few or no commercial examples currently.
• RAID-7. This type includes a real-time embedded operating system as a controller, caching via a high-speed bus, and other characteristics of a stand-alone computer. One vendor offers this system.
• RAID-10. This type offers an array of stripes in which each stripe is a RAID-1 array of drives. This offers higher performance than RAID-1 but at much higher cost.
• RAID-53. This type offers an array of stripes in which each stripe is a RAID-3 array of disks. This offers higher performance than RAID-3 but at much higher cost.

Rambus Dynamic Random Access Memory (RDRAM) is a memory subsystem that promises to transfer up to 1.6 billion bytes per second. The subsystem consists of the RAM, the RAM controller, and the bus (path) connecting RAM to the microprocessor and devices in the computer that use it. Direct Rambus (DRDRAM), a technology developed and licensed by the Rambus Corporation, will be used with Intel microprocessors beginning in 1999. High-speed RAM is expected to accelerate the growth of visually intensive interfaces such as 3-D, interactive games, and streaming multimedia. Rambus is intended to replace the current main memory technology of dynamic random access memory (DRAM). Much faster data transfer rates from attached devices such as videocams using Firewire and the Accelerated Graphics Port (AGP) make it important to reduce the bottleneck in getting data into the computer, staging it in RAM, and moving it throught the microprocessor and to the display or other output devices.

Direct Rambus (DRDRAM) provides a two-byte (16 bit) bus rather than DRAM's 8-bit bus. At a RAM speed of 800 megahertz (800 million cycles per second), the peak data transfer rate is 1.6 billion bytes per second. Direct Rambus uses pipelining to move data from RAM to cache memory levels that are closer to the microprocessor or display. Up to eight operations may be underway at the same time. Rambus is designed to fit into existing motherboard standards. The components that are inserted into motherboard connections are called Rambus in-line memory modules (RIMMs). They can replace conventional DIMMs.

A proposed alternative to DRDRAM is SyncLink DRAM (SLDRAM).
 
 

RAMDAC (random access memory digital-to-analog converter) is a microchip that converts digital image data into the analog data needed by a computer display. A RAMDAC microchip is built into the video adapter in a computer. It combines a small static RAM (SRAM) containing a color table with three digital-to-analog converters (DACs) that change digital image data into analog signals that are sent to the display's color generators, one for each primary color - red, green, and blue. In a cathode ray tube (CRT) display, an analog signal is sent to each of three electron guns. With displays using other technologies, the signals are sent to a corresponding mechanism.

How It Works

For displays with true color, the digital color data is fed directly to the DACs, bypassing the SRAM table, which is not needed.
 
 

Remote access is the ability to get access to a computer or a network from a remote distance. In corporations, people at branch offices, telecommuters, and people who are travelling may need access to the corporation's network. Home users get access to the Internet through remote access to an Internet service provider (ISP). Dial-up connection through desktop, notebook, or handheld computer modems over regular telephone lines is a common method of remote access. Remote access is also possible using a dedicated line between a computer or a remote local area network and the "central" or main corporate local area network. A dedicated line is more expensive and less flexible but offers faster data rates. ISDN is a common method of remote access from branch offices since it combines dial-up with faster data rates. Wireless, cable modem, and DSL technologies offer other possibilities for remote access.

A remote access server is the computer and associated software that is set up to handle users seeking access to network remotely. Sometimes called a communication server, a remote access server usually includes or is associated with a firewall server to ensure security and a router that can forward the remote access request to another part of the corporate network.

A remote access server may include or work with a modem pool manager so that a small group of modems can be shared among a large number of intermittently present remote access users.
 
 

Rambus Dynamic Random Access Memory (RDRAM) is a memory subsystem that promises to transfer up to 1.6 billion bytes per second. The subsystem consists of the RAM, the RAM controller, and the bus (path) connecting RAM to the microprocessor and devices in the computer that use it. Direct Rambus (DRDRAM), a technology developed and licensed by the Rambus Corporation, will be used with Intel microprocessors beginning in 1999. High-speed RAM is expected to accelerate the growth of visually intensive interfaces such as 3-D, interactive games, and streaming multimedia. Rambus is intended to replace the current main memory technology of dynamic random access memory (DRAM). Much faster data transfer rates from attached devices such as videocams using Firewire and the Accelerated Graphics Port (AGP) make it important to reduce the bottleneck in getting data into the computer, staging it in RAM, and moving it throught the microprocessor and to the display or other output devices.

Direct Rambus (DRDRAM) provides a two-byte (16 bit) bus rather than DRAM's 8-bit bus. At a RAM speed of 800 megahertz (800 million cycles per second), the peak data transfer rate is 1.6 billion bytes per second. Direct Rambus uses pipelining to move data from RAM to cache memory levels that are closer to the microprocessor or display. Up to eight operations may be underway at the same time. Rambus is designed to fit into existing motherboard standards. The components that are inserted into motherboard connections are called Rambus in-line memory modules (RIMMs). They can replace conventional DIMMs.

A proposed alternative to DRDRAM is SyncLink DRAM (SLDRAM).
 
 

1) In the Microsoft Windows 95, Windows 98, and Windows NT operating systems, the Registry is a single place for keeping such information as what hardware is attached, what system options have been selected, how computer memory is set up, and what application programs are to be present when the operating system is started. The Registry is somewhat similar to and a replacement for the simpler INI (initialization) and configuration files used in earlier Windows systems. INI files are still supported, however, for compatibility with the 16-bit applications written for earlier systems.

In general, the user updates the Registry indirectly using Control Panel tools, such as Tweak UI. When you install or uninstall application programs, they also update the Registry. In a network environment, Registry information can be kept on a server so that system policies for individuals and workgroups can be managed centrally.

2) The Internet Registry manages the Internet's domain name system. It is supervised by the Internet Architecture Board of the Internet Society.
 
 

1) In telecommunication networks, a repeater is a device that receives a signal on an electromagnetic or optical transmission medium, amplifies the signal, and then retransmits it along the next leg of the medium. Repeaters overcome the attenuation caused by free-space electromagnetic-field divergence or cable loss. A series of repeaters make possible the extension of a signal over a distance. Repeaters are used to interconnect segments in a local area network (LAN). They're also used to amplify and extend wide area network transmission on wire and wireless media.

In his Telecom Dictionary, Harry Newton points out that, in addition to strengthening the signal, repeaters also remove the "noise" or unwanted aspects of the signal. According to Newton, repeaters can do this with digital signals because, unlike analog signals, the original signal, even if weak or distorted, can be clearly perceived and restored. With analog transmission, signals are restrengthened with amplifiers which unfortunately also amplify noise as well as information.

Because digital signals depend on the presence or absence of voltage, they tend to dissipate more quickly than analog signals and need more frequent repeating. Whereas analog signal amplifiers are spaced at 18,000 meter intervals, digital signal repeaters are typically placed at 2,000 to 6,000 meter intervals.

In a cable system, a repeater can be simple, consisting of an amplifier circuit and a couple of signal transformers. The impedance of the cable must be matched to the input and output of the amplifier to optimize the efficiency of the amplifier. Impedance matching also minimizes reflection of signals along the cable. Such reflection can produce undesirable echo effects.

In a wireless communications system, a repeater consists of a radio receiver, an amplifier, a transmitter, an isolator, and two antennas. (See illustration A.) The transmitter produces a signal on a frequency that differs from the received signal. This so-called frequency offset is necessary to prevent the strong transmitted signal from disabling the receiver. The isolator provides additional protection in this respect. A repeater, when strategically located on top of a high building or a mountain, can greatly enhance the performance of a wireless network by allowing communications over distances much greater than would be possible without it.

In a fiber optic network, a repeater consists of a photocell, an amplifier, and a light-emitting diode (LED) or infrared-emitting diode (IRED) for each light or IR signal that requires amplification. (See illustration B.) Fiber optic repeaters operate at power levels much lower than wireless repeaters, and are also much simpler and cheaper. However, their design requires careful attention to ensure that internal circuit noise is minimized.

2) A bus repeater links one computer bus to a bus in another computer chassis, essentially chaining one computer to another.

3) Repeaters are commonly used by amateur and commercial radio operators to extend signals in the radio frequency range from one receiver to another. These consist of drop repeaters, similar to the cells in cellular radio, and hub repeaters, which receive and retransmit signals from and to a number of directions.
 
 

Replication (pronounced rehp-lih-KA-shun) is the process of making a replica (a copy) of something. A replication (noun) is a copy. The term is used in fields as varied as microbiology (cell replication), knitwear (replication of knitting patterns), and information distribution (CD-ROM replication).

On the Internet, a Web site that has been replicated in its entirety and put on another site is called a mirror site.

Using the groupware product, Lotus Notes, replication is the periodic electronic refreshing (copying) of a database from one computer server to another so that all users in the Notes network constantly share the same level of information.
 
 

In information technology, a repository (pronounced ree-PAHZ-ih-tor-i) is a central place in which an aggregation of data is kept and maintained in an organized way, usually in computer storage. The term is from the Latin repositorium, a vessel or chamber in which things can be placed, and it can mean a place where things are collected. Depending on how the term is used, a repository may be directly accessible to users or may be a place from which specific databases, files, or documents are obtained for further relocation or distribution in a network. A repository may be just the aggregation of data itself into some accessible place of storage or it may also imply some ability to selectively extract data. Related terms are data warehouse and data mining.
 
 

A RISC (reduced instruction set computer) is a microprocessor that is designed to perform a smaller number of types of computer instructions so that it can operate at a higher speed (perform more MIPS, or millions of instructions per second). Since each instruction type that a computer must perform requires additional transistors and circuitry, a larger list or set of computer instructions tends to make the microprocessor more complicated and slower in operation.

John Cocke of IBM Research in Yorktown, New York, originated the RISC concept in 1974 by proving that about 20% of the instructions in a computer did 80% of the work. The first computer to benefit from this discovery was IBM's PC/XT in 1980. Later, IBM's RISC System/6000, made use of the idea. The term itself (RISC) is credited to David Petersen, a teacher at the University of California in Berkeley. The concept was used in Sun Microsystems' SPARC microprocessors and led to the founding of what is now MIPS Technologies, part of Silicon Graphics. DEC's Alpha microchip also uses RISC technology.

The RISC concept has led to a more thoughtful design of the microprocessor. Among design considerations are how well an instruction can be mapped to the clock speed of the microprocessor (ideally, an instruction can be performed in one clock cycle); how "simple" an architecture is required; and how much work can be done by the microchip itself without resorting to software help.

Besides performance improvement, some advantages of RISC and related design improvements are:

• A new microprocessor can be developed and tested more quickly if one of its aims is to be less complicated.
• Operating system and application programmers who use the microprocessor's instructions will find it easier to develop code with a smaller instruction set.
• The simplicity of RISC allows more freedom to choose how to use the space on a microprocessor.
• Higher-level language compilers produce more efficient code than formerly because they have always tended to use the smaller set of instructions to be found in a RISC computer.

RJ (registered jacks, sometimes described as RJ-XX) is a series of telephone connection interfaces (receptacle and plug) that are registered with the U.S. Federal Communications Commission (FCC). They derive from interfaces that were part of AT&T's Universal Service Order Codes (USOC) and were adopted as part of FCC regulations (specifically Part 68, Subpart F. Section 68.502). The term jack sometimes means both receptacle and plug and sometimes just the receptacle.

RJ-11

The four wires are usually characterized as a red and green pair and a black and white pair. The red and green pair typically carry voice or data. On an outside phone company connection, the black and white pair may be used for low-voltage signals such as phone lights. On a PBX system, they may be used for other kinds of signaling.

Your computer modem is usually connected to an RJ-11 jack.
 

RJ-14

RJ-45

There are two varieties of RJ-45: keyed and unkeyed. Keyed has a small bump on its end and the female complements it. Both jack and plug must match.
 
 

Roaming service is the ability to get access to the Internet when away from home at the price of a local call or at a charge considerably less than the regular long-distance charges. For example, if you normally get access to the Internet from an access provider in Brooklyn, New York and are travelling to Hong Kong, you can call a designated access provider in Hong Kong. Instead of paying long distance charges to your local provider in Brooklyn, you pay the local phone connection charge in Hong Kong and possibly a modest additional charge for the service.

Roaming service is made possible through Internet service providers (ISPs) who have cooperative agreements to grant each others' customers local access to the Internet. Special software allows cooperating ISPs to keep track of and calculate prearranged payments for usage differences. Here's how it works for the user:

1. The Internet user must already subscribe to an ISP that offers roaming service arrangements.
2. Assuming the ISP does, the user can determine a cooperating ISP in a city to which the user is travelling.
3. In the travel location, the user can call the local ISP's designated phone number through the computer modem, entering information during login that will identify the user's home ISP.
4. The "foreign" ISP will contact the ISP and determine that the user is a valid user.
5. The "foreign" ISP will grant the user access to the Internet. The user will be able to access e-mail from the home mail server.
6. The user will be charged at local phone rates. In addition, depending on the particular service arrangement, the home ISP may levy an additional hourly usage charge of several dollars an hour or a monthly charge in case the service is used during that month.

If you are travelling and simply need to be able to exchange e-mail, you can consider getting a freemail membership (usually free) from HotMail, Rocketmail, or other freemail providers. Hotmail also offers POP3 server accounts for access to up to four e-mail accounts you may already have, assuming you remember the POP3 server name and your user IDs and passwords.

If you subscribe to a somewhat global service such as AT&T's WorldNet or the IBM Global Network, you may already be able to access your account in certain cities through your provider's local point-of-presence (POP) on the Internet without having to pay for a long-distance call.
 
 

On the Internet, a router is a device or, in some cases, software in a computer, that determines the next network point to which a packet should be forwarded toward its destination. The router is connected to at least two networks and decides which way to send each information packet based on its current understanding of the state of the networks it is connected to. A router is located at any juncture of networks or gateway, including each Internet point-of-presence. A router is often included as part of a network switch.

A router creates or maintains a table of the available routes and their conditions and uses this information along with distance and cost algorithms to determine the best route for a given packet. Typically, a packet may travel through a number of network points with routers before arriving at its destination. An edge router is a router that interfaces with an asynchronous transfer mode (ATM) network. A brouter is a network bridge combined with a router.
 
 

A real-time operating system (RTOS) is an operating system that guarantees a certain capability within a specified time constraint. For example, an operating system might be designed to ensure that a certain object was available for a robot on an assembly line. In what is usually called a "hard" real-time operating system, if the calculation could not be performed for making the object available at the designated time, the operating system would terminate with a failure. In a "soft" real-time operating system, the assembly line would continue to function but the production output might be lower as objects failed to appear at their designated time, causing the robot to be temporarily unproductive. Some real-time operating systems are created for a special application and others are more general purpose. Some existing general purpose operating systems claim to be a real-time operating systems. To some extent, almost any general purpose operating system such as Microsoft's Windows NT or IBM's OS/390 can be evaluated for its real-time operating system qualities. That is, even if an operating system doesn't qualify, it may have characteristics that enable it to be considered as a solution to a particular real-time application problem.

In general, real-time operating systems are said to require:

• Multitasking
• Process threads that can be prioritized
• A sufficient number of interrupt levels

Synchronous DRAM (SDRAM) is a generic name for various kinds of DRAM that are synchronized with the clock speed that the microprocessor is optimized for. This tends to increase the number of instructions that the processor can perform in a given time. The speed of SDRAM is rated in MHz rather than in nanoseconds (ns). This makes it easier to compare the bus speed and the RAM chip speed. You can convert the RAM clock speed to nanoseconds by dividing the chip speed into 1 billion ns (which is one second). For example, an 83 MHz RAM would be equivalent to 12 ns.
 
 

A set-top box is a device that enables a television set to become a user interface to the Internet. A set-top box is really a specialized computer that can "talk to" the Internet - that is, it contains a Web browser (which is really a Hypertext Transfer Protocol client) and the Internet's main program, TCP/IP.

The service to which the set-top box is attached may be through a telephone line as, for example, with Web TV, or through a cable TV company like TCI.
 
 

Synchronous Graphics RAM (SGRAM) is clock-synchronized RAM that is used for video memory. It is relatively low-cost video memory. It uses masked write, which enables selected data to be modified in a single operation rather as a sequence of read, update, and write operations. It also uses block write, which allows data for background or foreground image fills to be handled more efficiently. SGRAM is single-ported. Its special features are what make it a moderately fast form of video memory. The Matrox Mystique is an example of a video card that uses SGRAM.
 
 

Shadow RAM is a copy of Basic Input/Output Operating System (BIOS) routines from read-only memory (ROM) into a special area of random access memory (RAM) so that they can be accessed more quickly. Access in shadow RAM is typically in the 60-100 nanosecond range whereas ROM access is in the 125-250 ns range. In some operating systems such as DOS, certain BIOS routines are not only used during the booting or startup of the system, but also during normal operation, especially to drive the video display unit. In Windows and OS/2, however, these routines are not used and the use of shadow RAM is not necessary. In some systems, the user can turn the use of shadow RAM off or on.
 
 

A Web file with the suffix of ".shtml" (rather than the usual ".htm") indicates a file that includes some information that will be added "on the fly" by the server before it is sent to you. A typical use is to include a "Last modified" date at the bottom of the page.

This HTTP facility is referred to as a server-side include. (Although rarely done, the server administrator can identify some other file name suffix than ".shtml" as a server-side include file.) You can think of a server-side include as a limited form of Common Gateway Interface (CGI) application. In fact, the CGI is not used. The server simply searches the server-side include file for CGI environment variables, and inserts the variable information in the places in the file where the "include" statements have been inserted.)

When creating a Web site, a good idea is to ask your server administrator which environment variables can be used and whether the administrator can arrange to set the server up so that these can be handled. Your server administrator should usually be able to help you insert the necessary include statements in an HTML file.
 
 

A SIMM is a module containing one or several random access memory (RAM) chips on a small circuit board with pins that connect to the computer motherboard. Since the more RAM your computer has, the less frequently it will need to access your secondary storage (for example, hard disk or CD-ROM), PC owners sometimes expand RAM by installing additional SIMMs. SIMMs typically come with a 32 data bit (36 bits counting parity bits) path to the computer that requires a 72-pin connector. SIMMs usually come in memory chip multiples of four megabytes.

The memory chips on a SIMM are typically dynamic RAM (DRAM) chips. An improved form of RAM called Synchronous DRAM (SDRAM) can also be used. Since SDRAM provides a 64 data bit path, it requires at least two SIMMs or a dual in-line memory module (DIMM).
 
 

SLIP is a TCP/IP protocol used for communication between two machines that are previously configured for communication with each other. For example, your Internet server provider may provide you with a SLIP connection so that the provider's server can respond to your requests, pass them on to the Internet, and forward your requested Internet responses back to you. Your dial-up connection to the server is typically on a slower serial line rather than on the parallel or multiplex lines such as a T-1 line of the network you are hooking up to.

A better service is provided by the Point-to-Point Protocol (PPP).
 
 

Slot 1 and Slot 2 are names for the way Intel P6-based microprocessors connect to a computer motherboard so that it makes contact with the built-in paths called the data bus. Slot 1 and Slot 2 were developed by Intel as a replacement for its Zero Insertion Force (ZIF) sockets, the most familiar of which is Socket 7 for Intel's Pentium processors. For the Pentium II, which is based on Intel's P6 micro architecture, Intel switched to the Slot 1 configuration. With the slot approach, the microprocessor is packaged in a cartridge, known as a Single Edge Cartridge, that is easily inserted into a slot designed into the motherboard. The new approach will make connection to the faster and larger number of data paths in future processors more feasible.

Officially, Intel now refers to Slot 1 as the 242-contact slot connector and Slot 2 as the 330-contact slot connector. Besides the Pentium II, Intel's Celeron processor also uses the Slot 1 configuration. Intel's high-end Pentium II Xeon processor uses the Slot 2 configuration. Intel is said to be developing a Slot M.

Since the motherboards are different, computer owners with Socket 7 Pentiums will not be able to upgrade to the newer P6 Pentiums with Slot 1 and Slot 2 configurations. AMD and Cyrix, which offer processors that compete with the Pentium II, say they plan to continue using the Socket 7 motherboard.
 
 

S.M.A.R.T. (Self-Monitoring Analysis and Reporting Technology) is an interface between a computer's start-up program or BIOS and the computer hard drive. It is a feature of the Enhanced Integrated Drive Electronics (EIDE) technology that controls access to the hard drive. If S.M.A.R.T is enabled when a computer is set up, the BIOS can receive analytical information from the hard drive and determine whether to send the user a warning message about possible future failure of the hard drive.
 
 

SMTP (Simple Mail Transfer Protocol) is a TCP/IPprotocol used in sending and receiving e-mail. However, since it's limited in its ability to queue messages at the receiving end, it's usually used with one of two other protocols, POP3 or IMAP, that let the user save messages in a server mailbox and download them periodically from the server. In other words, users typically use a program that uses SMTP for sending e-mail and either POP3 or IMAP for receiving messages that have been received for them at their local server. Most mail programs such as Eudora let you specify both an SMTP server and a POP server. On UNIX-based systems, sendmail is the most widely-used SMTP server for e-mail. A commercial package, Sendmail, includes a POP3 server and also comes in a version for Windows NT.

SMTP usually is implemented to operate over TCPport 25. The details of SMTP are in RFC 821 of the Internet Engineering Task Force (IETF). An alternative to SMTP that is widely used in Europe is X.400.
 
 

Snail mail is a slang term for the regular postal service (for example, the U.S. Postal Service) with the implication that it is a lot slower than e-mail. It's worth noting, perhaps, that in the early days of the Internet, it was proposed that the (then) U. S. Post Office manage e-mail. Electronic messages would come to your local post office and then be delivered to you along with the regular mail. The proposal was not considered for very long.

Snail mail or not, one must acknowledge that regular postal services offer a number of valuable services not likely to be available soon on the World Wide Web.
 
 

Socket 7 is the descriptive term for the way certain Intel Pentium microprocessors plug into a computer motherboard so that it makes contact with the motherboard's built-in wires or data bus. Socket 7 is the best-known of eight connection variations that use the Zero Insertion Force (ZIF) socket. As its name implies, the ZIF socket is designed for ease of manufacture and so that the average computer owner will be able to upgrade the microprocessor. The ZIF socket contains a lever that opens and closes, securing the microprocessor in place. Various sockets have a differing number of pins and pin layout arrangements.

For its Pentium II processor, Intel has moved from the socket configuration to an approach in which the processor is packaged in a cartridge and fits into a slot in the motherboard. There are two sizes, Slot 1 and Slot 2. AMD and Cyrix, which offer competitive processors, continue to use the Socket 7 arrangement.

The following table summarizes the socket characteristics for different Intel processors.

Socks (or "SOCKS") is a protocol that a proxy server can use to accept requests from client users in a company's network so that it can forward them across the Internet. Socks uses sockets to represent and keep track of individual connections. The client side of Socks is built into certain Web browsers and the server side can be added to a proxy server.

A socks server handles requests from clients inside a company's firewall and either allows or rejects connection requests, based on the requested Internet destination or user identification. Once a connection and a subsequent "bind" request have been set up, the flow of information exchange follows the usual protocol (for example, the Web's HTTP protocol).
 
 

S/PDIF (Sony/Philips Digital Interface) is a standard audio transfer file format. It is usually found on digital audio equipment such as a DAT machine or audio processing device. It allows the transfer of audio from one file to another without the conversion to and from an analog format, which could degrade the signal quality.

The most common connector used with an S/PDIF interface is the RCA connector, the same one used for consumer audio products. An optical connector is also sometimes used.
 
 

SRAM (static RAM) is random access memory (RAM) that retains data bits in its memory as long as power is being supplied. Unlike dynamic RAM (DRAM), which stores bits in cells consisting of a capacitor and a transistor, SRAM does not have to be periodically refreshed. Static RAM provides faster access to data and is more expensive than DRAM. SRAM is used for a computer's cache memory and as part of the RAMDAC on a video card.
 
 

A stackable hub is a hub designed to be connected and stacked or positioned on top of another hub, forming an expanding stack. Since a hub is basically a concentrator of device connections, a set of stackable hubs is just a bigger concentrator. The stackable approach allows equipment to be easily and economically expanded as a local area network grows in size. The stacking feature also reduces clutter.

Typically, devices with network interface cards (NICs) are connected to each hub with shielded twisted pair (STP) or unshielded twisted pair (UTP) cable. The set of stackable hubs is interconnected with a very short "cascading" cable in the rear of the stack. A special port, such as an Ethernet Attachment Unit Interface (AUI) port, may be provided to connect the set of stackable hubs to a backbone cable that connects to other sets of stackable hubs or other network devices.

Typical stackable hub options include:

• The ability to mix hubs, routers, and other devices in the same stack
• Fault tolerance so that if one hub fails, the other hubs in the stack can continue to operate
• Port redundancy so that if one port fails, a backup port can be automatically substituted
• Hardware and software to let you manage the stackable hubs using the Simple Network Management Protocol (SNMP)

The T-carrier system, introduced by the Bell System in the U.S. in the 1960s, was the first successful system that supported digitized voice transmission. The original transmission rate (1.544 Mbps) in the T-1 line is in common use today in Internet service provider (ISP) connections to the Internet. Another level, the T-3 line, providing 44.736 Mbps, is also commonly used by ISPs. Another commonly installed service is a fractional T-1 line, which is the rental of some portion of the 24 channels in a T-1 line, with the other channels going unused.

The T-carrier system is entirely digital, using pulse code modulation and time-division multiplexing. The system uses four wires and provides full-duplex capability (two wires for receiving and two for sending at the same time). The T-1 digital stream consists of 24 64-Kbps channels that are multiplexed. (The standardized 64 Kbps channel is based on the bandwidth required for a voice conversation.) The four wires were originally a pair of twisted-pair copper wires, but can now also include coaxial cable, optical fiber, digital microwave, and other media. A number of variations on the number and use of channels are possible.

In the T-1 system, voice signals are sampled 8,000 times a second and each sample is digitized into an 8-bit word. With 24 channels being digitized at the same time, a 192-bit frame (24 channels each with an 8-bit word) is thus being transmitted 8,000 times a second. Each frame is separated from the next by a single bit, making a 193-bit block. The 192 bit frame multiplied by 8,000 and the additional 8,000 framing bits make up the T-1's 1.544 Mbps data rate. The signaling bits are the least significant bits per frame.
 
 

TCP/IP (Transmission Control Protocol/Internet Protocol) is the basic communication language or protocol of the Internet. It can also be used as a communications protocol in the private networks called intranets and in extranets. When you are set up with direct access to the Internet, your computer is provided with a copy of the TCP/IP program just as every other computer that you may send messages to or get information from also has a copy of TCP/IP.

TCP/IP is a two-layered program. The higher layer, Transmission Control Protocol, manages the assembling of a message or file into smaller packets that are transmitted over the Internet and received by a TCP layer that reassembles the packets into the original message. The lower layer, Internet Protocol, handles the address part of each packet so that it gets to the right destination. Each gateway computer on the network checks this address to see where to forward the message. Even though some packets from the same message are routed differently than others, they'll be reassembled at the destination.

TCP/IP uses the client/server model of communication in which a computer user (a client) requests and is provided a service (such as sending a Web page) by another computer (a server) in the network. TCP/IP communication is primarily point-to-point, meaning each communication is from one point (or host computer) in the network to another point or host computer. TCP/IP and the higher-level applications that use it are collectively said to be "connectionless" because each client request is considered a new request unrelated to any previous one (unlike ordinary phone conversations that require a dedicated connection for the call duration). Being connectionless frees network paths so that everyone can use them continuously. (Note that the TCP layer itself is not connectionless as far as any one message is concerned. Its connection remains in place until all packets in a message have been received.)

Many Internet users are familiar with the even higher layer application protocols that use TCP/IP to get to the Internet. These include the World Wide Web's Hypertext Transfer Protocol (HTTP), the File Transfer Protocol (FTP), Telnet (Telnet) which lets you logon to remote computers, and the Simple Mail Transfer Protocol (SMTP). These and other protocols are often packaged together with TCP/IP as a "suite."

Personal computer users usually get to the Internet through the Serial Line Internet Protocol (SLIP) or the Point-to-Point Protocol (PPP). These protocols encapsulate the IP packets so that they can be sent over a dial-up phone connection to an access provider's modem.

Protocols related to TCP/IP include the User Datagram Protocol (UDP), which is used instead of TCP for special purposes. Other protocols are used by network host computers for exchanging router information. These include the Internet Control Message Protocol (ICMP), the Interior Gateway Protocol (IGP), the Exterior Gateway Protocol (EGP), and the Border Gateway Protocol (BGP).
 
 

Telnet is the way you can access someone else's computer, assuming they have given you permission. (Such a computer is frequently called a host computer.) More technically, Telnet is a user command and an underlying TCP/IP protocol for accessing remote computers. The Web or HTTP protocol and the FTP protocol allow you to request specific files from remote computers, but not to actually be logged on as a user of that computer. With Telnet, you log on as a regular user with whatever privileges you may have been granted to the specific applications and data on that computer.
 
 

A display screen made with TFT (thin film transistor) technology is a liquid crystal display (LCD), common in notebook and laptop computers, that has a transistor for each pixel (that is, for each of the tiny elements that control the illumination of your display). Having a transistor at each pixel means that the current that triggers pixel illumination can be smaller and therefore can be switched on and off more quickly.

TFT is also known as active matrix technology (and contrasted with "passive matrix" which does not have a transistor at each pixel). A TFT or active matrix display is more responsive to change. For example, when you move your mouse across the screen, a TFT display is fast enough to reflect the movement of the mouse cursor. (With a passive matrix display, the cursor temporarily disappears until the display can "catch up.")
 
 

TFTP (Trivial File Transfer Protocol) is a network application that is simpler than the File Transfer Protocol (FTP) but less capable. It is used where user authentication and directory visibility are not required. TFTP uses the User Datagram Protocol (UDP) rather than the Transmission Control Protocol (TCP). TFTP is described formally in RFC 1350.
 
 

Thicknet and Thinnet (sometimes spelled ThickNet and ThinNet) are commonly used terms for the larger and smaller size of coaxial cable used in Ethernet local area networks. Thicknet, also known as Thickwire, is 0.4 inches in diameter and has 50 ohms of electromagnetic impedance. Thinnet, also known as Thinwire and Cheapernet, is 0.2 inches in diameter with the same impedance as Thickwire. Thicknet was the original Ethernet wiring, but Thinnet, which is cheaper and can be installed more easily, is the more commonly installed Ethernet wire. Thicknet continues to be used for backbone wiring. An alternative to Thinnet on an Ethernet network is twisted pair.
 
 

"Thin client" is a synonym for the Net PC or the network computer (NC), personal computers for businesses that are designed to be centrally-managed, configured with only essential equipment, and devoid of CD-ROM players, diskette drives, and expansion slots (and therefore lower in cost). The term derives from the fact that small computers in networks tend to be clients of local area network and other servers. Since the idea is to limit the capabilities of these computers to only essential applications, they will tend to be purchased and remain "thin" in terms of the client applications they include.

The term "thin client" seems to be used as a synonym for both the Net PC and the network computer (NC), which are somewhat different concepts. The Net PC is based on Intel microprocessors and Windows software (Intel was a leader in defining the Net PC specification). The network computer (NC) is a concept backed by Oracle and Sun Microsystems that may or may not use Intel microprocessors and would use a Java-based operating system.

The thin client idea recognizes a corporate need for a lowest-cost PC dedicated to specific applications. The demand for thin client computers and servers to serve them is expected to develop rapidly during 1998.
 
 

In the computer industry, a thin server is a PC that contains just enough hardware and software to support a particular function that users can share in a network, such as access to files on a storage device, access to CD-ROM drives, printing, or Internet access. According to the first companies who have used the term, a thin server can be quickly added to a network and costs less than providing the same service through a more general-purpose computer server. Usually, a thin server contains an abbreviated version of one or more operating systems, such as Windows 95, Macintosh, or UNIX, and necessary network protocols, such as TCP/IP and NetBEUI. Typically, it also includes HTTP so that it can be configured, administered, and used through a Web browser user interface. The hardware processor sometimes uses RISC processing.

Some thin servers are designed and marketed for use on local area networks in businesses. A newer development is a thin server intended for home use. Data General makes a thin server for the home or small office that performs the single function of providing access to the Internet. Other desktop and notebook computers and possibly other electronic appliances can be hooked up as clients and share the thin server's connection or connections to the Internet.

The thin server and the thin client concepts arise from the same idea: why pay for the function in a computer that you don't need? Whereas the thin client is a constrained personal computer that gets applications and data the user needs from a shared and usually full-function server computer, the thin server serves the client requests of other computers and their users, doing one thing well without needing to provide any other service. A thin server is similar to a thin client in that both may be thought of as single application, special-purpose computers, almost always with a very limited storage capability and with "trimmed-down" operating systems.

According to a 1998 Dataquest study, the thin server market is expected to grow to $16 billion (US) in the year 2000.
 
 

Thicknet and Thinnet (sometimes spelled ThickNet and ThinNet) are commonly used terms for the larger and smaller size of coaxial cable used in Ethernet local area networks. Thicknet, also known as Thickwire, is 0.4 inches in diameter and has 50 ohms of electromagnetic impedance. Thinnet, also known as Thinwire and Cheapernet, is 0.2 inches in diameter with the same impedance as Thickwire. Thicknet was the original Ethernet wiring, but Thinnet, which is cheaper and can be installed more easily, is the more commonly installed Ethernet wire. Thicknet continues to be used for backbone wiring. An alternative to Thinnet on an Ethernet network is twisted pair.
 
 

UDP (User Datagram Protocol) is a communications method (protocol) that offers a limited amount of service when messages are exchanged between computers in a network that uses the Internet Protocol (IP). UDP is an alternative to the Transmission Control Protocol (TCP) and, together with IP, is sometimes referred to as UDP/IP. Like the Transmission Control Protocol, UDP uses the Internet Protocol to actually get a data unit (called a datagram) from one computer to another. Unlike TCP, however, UDP does not provide the service of dividing a message into packets (datagrams) and reassembling it at the other end. Specifically, UDP doesn't provide sequencing of the packets that the data arrives in. This means that the application program that uses UDP must be able to make sure that the entire message has arrived and is in the right order. Network applications that want to save processing time because they have very small data units to exchange (and therefore very little message reassembling to do) may prefer UDP to TCP. The Trivial File Transfer Protocol (TFTP) uses UDP instead of TCP.

UDP provides two services not provided by the IP layer. It provides port numbers to help distinguish different user requests and, optionally, a checksum capability to verify that the data arrived intact.

In the Open Systems Interconnection (OSI) communication model, UDP, like TCP, is in layer 4, the Transport Layer.
 
 

The "universal network" is the idea of a single network that integrates the existing voice and public telecommunications network (including the Internet), cable TV, data networks, and video broadcast networks so that they work together well. Currently, each has a different kind of traffic and the older networks bear the burden of an out-of-date infrastructure. For example, the public voice network supports connections of phone-call duration and circuit-switching (although the same network also supports connectionless traffic and packet-switching for data). The video broadcast and cable TV networks deliver mainly the higher-bandwidth continous-flow traffic of streaming video and sound.

Juniper Networks plans something close to a universal network in a new fiber-optic network that will include very fast (multigigabit) switching using microchips that are customized for Internet traffic. The microchips will include application-specific (ASIC) circuits made by IBM. The switches use wave-division multiplexing (WDM).

Several large companies have invested over $60 million dollars in Juniper, a company whose 85 employees are mainly optoelectronic engineers. In early 1998, specific product plans hadn't yet been unveiled.
 
 

USB (Universal Serial Bus) is a "plug-and-play" interface between a computer and add-on devices (such as audio players, joysticks, keyboards, telephones, scanners, and printers). With USB, a new device can be added to your computer without having to add an adapter card or even having to turn the computer off. The USB peripheral bus standard was developed by Compaq, IBM, DEC, Intel, Microsoft, NEC, and Northern Telecom and the technology is available without charge for all computer and device vendors.

USB supports a data speed of 12 megabits per second. This speed will accommodate a wide range of devices, including MPEG-2 video devices, data gloves, and digitizers. It is anticipated that USB will easily accommodate plug-in telephones that use ISDN and digital PBXs.

Since October, 1996, the Windows operating systems have been equipped with USB drivers or special software designed to work with specific I/O device types. USB is integrated into Windows 98. Today, most new computers and peripheral devices are equipped with USB.

A different "plug-and-play" standard, Firewire/IEEE 1394, is designed to support much higher data rates and devices such as video camcorders and digital video disk (DVD) players. Both standards are expected to exist together, serving different device types.
 
 

Unshielded twisted pair is the most common kind of copper telephone wiring. Twisted pair is the ordinary copper wire that connects home and many business computers to the telephone company. To reduce crosstalk or electromagnetic induction between pairs of wires, two insulated copper wires are twisted around each other. Each signal on twisted pair requires both wires. Since some telephone sets or desktop locations require multiple connections, twisted pair is sometimes installed in two or more pairs, all within a single cable. For some business locations, twisted pair is enclosed in a shield that functions as a ground. This is known as shielded twisted pair (STP).

Twisted pair is now frequently installed with two pairs to the home, with the extra pair making it possible for you to add another line (perhaps for modem use) when you need it.

Twisted pair comes with each pair uniquely color coded when it is packaged in multiple pairs. Different uses such as analog, digital, and LAN Ethernet require different pair multiples.

Although twisted pair is often associated with home use, a higher grade of twisted pair is often used for horizontal wiring in LAN installations because it is less expensive than coaxial cable.

The wire you buy at a local hardware store for extensions from your phone or computer modem to a wall jack is not twisted pair. It is a side-by-side wire known as silver satin. The wall jack can have as many five kinds of hole arrangements or pinouts, depending on the kinds of wire the installation expects will be plugged in (for example, digital, analog, or LAN) . (That's why you may sometimes find when you carry your notebook computer to another location that the wall jack connections won't match your plug.)
 
 

Uuencode (also called Uuencode/Uudecode) is a popular utility for encoding and decoding files exchanged between users or systems in a network. It originated for use between users of UNIX systems (its name stood for "UNIX-to-UNIX encoding"). However, it's available or easily obtainable for use in all operating systems and most e-mail applications provide it as an encoding alternative, especially for e-mail attachments. If you're sending e-mail with an attachment and you suspect your recipient(s) may not have a MIME-compliant system (for example, an older PC or UNIX system), you may want to specify "Uuencode" for the attachment to an e-mail note. (In Eudora, when writing a note, look for the little box set to a default of "MIME" and change it to "Uuencode.")

Basically, what Uuencode does is to translate or convert a file or e-mail attachment (it can be an image, a text file, or a program) from its binary or bit-stream representation into the 7-bit ASCII set of text characters. Text can be handled by older systems that may not handle binary files well and larger files can be more easily divided into multi-part transmissions.

If your recipent is likely to be on an older Macintosh system, you may want to try sending the attachment in another format called BinHex.

A popular program for encoding and decoding files in Uuencode format is WinZip, which is shareware that you can download from the Winzip Web site.
 
 

A virtual area network (VAN) is a network on which users are enabled to share a more visual sense of community through high band-width connections. As conceived by PennWell Media Online, an online directory for specialized networking products, a virtual area network is something like a metropolitan area network (MAN) or extended local area network (LAN) in which all users can meet over high-bandwidth connections, enabling "face-to-face" online "coffeehouses," remote medical diagnosis and legal consultation, and online corporate or extracorporate workgroups, focus groups, and conferences. A VAN requires multi-megabyte data flow and can be implemented through the use of ADSL but more likely through the installation of cable modems. Since the high-bandwidth connections imply a common infrastructure, the first VANs are likely to be local or regional. However, a VAN can also be national or international in geographic scope, assuming all users share similar capabilities.
 
 

A virtual (or logical) LAN is a local area network with a definition that maps workstations on some other basis than geographic location (for example, by department, type of user, or primary application). The virtual LAN controller can change or add workstations and manage loadbalancing and bandwidth allocation more easily than with a physical picture of the LAN. Network management software keeps track of relating the virtual picture of the local area network with the actual physical picture.

VLANs are considered likely to be used with campus environment networks. Among companies likely to provide products with VLAN support are Cisco, Bay Networks, and 3Com.

There is a proposed VLAN standard, IEEE 802.10.
 
 

1) In the most recent computer usage, virtual machine is a term used by Sun Microsystems, developers of the Java programming language and runtime environment, to describe software that acts as an interface between compiled Java binary code and the microprocessor (or "hardware platform") that actually performs the program's instructions. Once a Java virtual machine has been provided for a platform, any Java program (which, after compilation, is called bytecode) can run on that platform. Java was designed to allow application programs to be built that could be run on any platform without having to be rewritten or recompiled by the programmer for each separate platform. Java's virtual machine makes this possible.

The Java virtual machine specification defines an abstract rather than a real "machine" (or processor) and specifies an instruction set, a set of registers, a stack, a "garbage-collected heap," and a method area. The real implementation of this abstract or logically defined processor can be in other code that is recognized by the real processor or be built into the microchip processor itself.

The output of "compiling" a Java source program (a set of Java language statements) is called bytecode. A Java virtual machine can either interpret the bytecode one instruction at a time (mapping it to a real microprocessor instruction) or the bytecode can be compiled further for the real microprocessor using what is called a just-in-time (JIT) compiler.

2) In IBM, a virtual machine is any multi-user shared-resource operating system that gives each user the appearance of having sole control of all the resources of the system.

3) In IBM, a virtual machine is also used to mean an operating system that is in turn managed by an underlying control progam. Thus, IBM's VM/ESA can control multiple virtual machines on an IBM S/390 system.

4) Elsewhere, virtual machine has been used to mean either an operating system or any program that runs a computer. We quote:

"A running program is often referred to as a virtual machine - a machine that doesn't exist as a matter of actual physical reality. The virtual machine idea is itself one of the most elegant in the history of technology and is a crucial step in the evolution of ideas about software. To come up with it, scientists and technologists had to recognize that a computer running a program isn't merely a washer doing laundry. A washer is a washer whatever clothes you put inside, but when you put a new program in a computer, it becomes a new machine.... The virtual machine: A way of understanding software that frees us to think of software design as machine design."

Virtual (or logical) memory is a concept that, when implemented by a computer and its operating system, allows programmers to use a very large range of memory or storage addresses for stored data. The computing system maps the programmer's virtual addresses to real hardware storage addresses. Usually, the programmer is freed from having to be concerned about the availability of data storage.

In addition to managing the mapping of virtual storage addresses to real storage addresses, a computer implementing virtual memory or storage also manages storage swapping between active storage (RAM) and hard disk or other high volume storage devices. Data is read in units called "pages" of sizes ranging from a thousand bytes (actually 1,024 decimal bytes) up to several megabyes in size. This reduces the amount of physical storage access that is required and speeds up overall system performance.
 
 

Virtual reality is the simulation of a real or imagined environment that can be experienced visually in the three dimensions of width, height, and depth and that may additionally provide an interactive experience visually in full real-time motion with sound and possibly with tactile and other forms of feedback. The simplest form of virtual reality is a 3-D image that can be explored interactively at a personal computer, usually by manipulating keys or the mouse so that the content of the image moves in some direction or zooms in or out. Most of these images require installing a plug-in for your browser. As the images become larger and interactive controls more complex, the perception of "reality" increases. More sophisticated efforts involve such approaches as wrap-around display screens, actual rooms augmented with wearable computers, and haptic joystick devices that let you feel the display images.

Virtual reality can be divided into:

• The simulation of real environments such as the interior of a building or a spaceship often with the purpose of training or education
• The development of an imagined environment, typically for a game or educational adventure

VoIP (voice over IP - that is, voice delivered using the Internet Protocol) is a term used in IP telephony for a set of facilities for managing the delivery of voice information using the Internet Protocol (IP). In general, this means sending voice information in digital form in discrete packets rather than in the traditional circuit-committed protocols of the public switched telephone network (PSTN). A major advantage of VoIP and Internet telephony is that it avoids the tolls charged by ordinary telephone service.

VoIP, now used somewhat generally, derives from the VoIP Forum, an effort by major equipment providers, including Cisco, VocalTec, 3Com, and Netspeak to promote the use of ITU-T H.323, the standard for sending voice (audio) and video using IP on the public Internet and within intranets. The Forum also promotes the user of directory service standards so that users can locate other users and the use of touch-tone signals for automatic call distribution and voice mail.

In addition to IP, VoIP uses the real-time protocol (RTP) to help ensure that packets get delivered in a timely way. Using public networks, it is currently difficult to guarantee Quality of Service (QoS). Better service is possible with private networks managed by an enterprise or by an Internet telephony service provider (ITSP).

A technique used by at least one equipment manufacturer, Netspeak, to help ensure faster packet delivery is to ping all possible network gateway computers that have access to the public network and choose the fastest path before establishing a TCP socket connection with the other end.

Using VoIP, an enterprise positions a "VoIP device" (such as Cisco's AS5300 access server with the VoIP feature) at a gateway. The gateway receives packetized voice transmissions from users within the company and then routes them to other parts of its intranet (local area or wide area network) or, using a T-1 or E-1 interface, sends them over the public switched telephone network.
 
 

A Web server is a program that, using the client/server model and the World Wide Web's Hypertext Transfer Protocol (HTTP), serves the files that form Web pages to Web users (whose computers contain HTTP clients that forward their requests). Every computer on the Internet that contains a Web site must have a Web server program. The most popular Web servers are Microsoft's Internet Information Server (IIS), which comes with the Windows NT server; Netscape's FastTrack and Enterprise servers; and Apache, a Web server for UNIX-based operating systems. Other Web servers include Novell's Web Server for users of its NetWare operating system and IBM's family of Lotus Domino servers, primarily for IBM's OS/390 and AS/400 customers.

Web servers often come as part of a larger package of Internet- and intranet-related programs for serving e-mail, downloading requests for FTP files, and building and publishing Web pages. Considerations in choosing a Web server include how well it works with the operating system and other servers, its ability to handle server-side programming, and publishing, search engine, and site building tools that may come with it.
 
 

WebTV, now owned by Microsoft, was one of the first entries in the much publicized convergence of the World Wide Web with television. You buy a set-top box similar to a cable TV box, then sign up with the WebTV access service and browse Web pages using a WebTV's browser and a hand-held control. A keyboard is provided optionally. WebTV uses your television set as an output device; the signals arrive, however, through a modem and a telephone line at 33.6 Kbps (Classic model) or 56 Kbps (Plus model).

There are two set-top boxes: the Classic, manufactured by Sony and Philips Magnavox and priced at $99, and the television-enhanced Plus, manufactured by Sony, Philips Magnavox, and Mitsubishi, priced at $199. A recent monthly connection charge was $19.95. For both models, the wireless keyboard is a $50 option, except that Mitsubishi bundles the keyboard with the set-top box and charges $250 for the package.

The most recent WebTV service includes support for frames (with certain limitations), JavaScript, RealAudio, Internet Relay Chat (IRC), and other Web technology.
 
 

WetPC (TM) is a wearable computer for underwater use. Developed by the Australian Institute of Marine Science, it allows a diver to gather and enter data immediately into a computer worn as part of the diver's gear. Instead of a keyboard or mouse, the diver interacts with the computer using a multi-button device worn at chest level and requiring only one hand. The display is attached to the diver's mask. The developers invented a new, easy-to-intuit human/computer interface that lets the user provide information in the form of multiple finger position combinations that are always visible on the display.
 
 

WinChip (also known as the WinChip C6) is a microprocessor designed for use in business computers that run Microsoft Windows operating systems Made by IDT, the microprocessor reportedly provides comparable performance to Intel's more expensive Pentium II microprocessors as well as to the more competitively-priced AMD-K6 and the Cyrix 6X86MX. IDT designed a smaller die area for the microprocessor, making it easier and cheaper to manufacture. WinChip cites Winstone tests that show the C6 has the highest rating per square millimeter of die area among Socket 7 microprocessors. The C6 does not include branch prediction and other features of some of the other microprocessors. It is optimized for running the most frequently used instructions and aims to be the most cost-effective choice for business applications such as word processing, spreadsheets, and database management.
 
 

Window RAM (WRAM), unrelated to Microsoft Windows, is very high-performance video RAM that is dual-ported and has about 25% more bandwidth than VRAM but costs less. It has features that make it more efficient to read data for use in block fills and text drawing. It can be used for very high resolution (such as 1600 by 1200 pixels) projection using true color. It's used in the Matrox Millenium video card.
 
 

WINS (Windows Internet Naming Service), part of the Microsoft Windows NT Server, manages the association of workstation names and locations with Internet Protocol addresses (IP addresses) without the user or an administrator having to be involved in each configuration change. WINS automatically creates a computer name-IP address mapping entry in a table, ensuring that the name is unique and not a duplicate of someone else's computer name. When a computer is moved to another geographic location, the subnet part of the IP address is likely to change. Using WINS, the new subnet information will be updated automatically in the WINS table. WINS complements the NT Server's Dynamic Host Configuration Protocol (DHCP), which negotiates an IP address for any computer (such as your workstation) when it is first defined to the network. If you're a computer user on a network connected to a Windows NT Server, you may find WINS mentioned in some of your network-related programs or system messages.

Based on Microsoft's paper, DHCP and WINS have been submitted to the Internet Engineering Task Force (IETF) as proposed open standards in Request for Comments 1533, 1534, 1541, and 1542. New features are included in the follow-on to Windows NT, Windows 2000.
 
 

Winsock is a programming interface and the supporting program that handles input/output requests for Internet applications in a Windows operating system. It's called Winsock because it's an adaptation for Windows of the Berkeley UNIX sockets interface. Sockets is a particular convention for connecting with and exchanging data between two program processes within the same computer or across a network.

Winsock runs between an application program such as a Netscape browser and the Internet program in your computer, TCP/IP. A request flows in the following order:

Winsock provides this interface for different versions of the Windows operating system. A comparable interface exists for Mac computers. Beginning with Windows 95, Winsock came as part of the operating system, but in earlier systems, a Winsock program had to be installed. UNIX systems do not require a Winsock equivalent because TCP/IP and its use of sockets was designed to run directly with UNIX application programs.

A number of companies offer a Winsock program, sometimes along with a suite of Internet protocol programs and applications. For example, Chameleon offers a suite that includes a Web browser, an FTP utility, a mail utility, and others. The Winsock program is included. The Trumpet Winsock is another popular stand-alone version. Winsock runs as a Windows dynamic link library (DLL) file. That is, it is loaded into the computer when an application needs it but doesn't need to be included as part of the application.

When you initially get set up with Internet access, you may need to make sure you have the right version of Winsock for your operating system and the applications provided by the access provider. If your operating system provides one version and the application suite provided by the access provider provides another, one version of Winsock may need to be removed.
 
 

Like Winsock, Winsock 2 is a programming interface and the supporting program that handles input/output requests for Internet applications in a Windows operating system. It's called Winsock because it's an adaptation for Windows of the Berkeley UNIX sockets interface. Sockets is a particular convention for connecting with and exchanging data between two progrram processes. Winsock 2 is a 32-bit version of Winsock.

Winsock 2 runs between an application program such as a Netscape browser and the Internet program in your computer, TCP/IP. A request flows in the following order:

Winsock 2 offers these advantages over Winsock:

• In addition to TCP/IP, it provides an interface to a variety of protocols, including IPX/SPX, ISDN, wireless protocols, and OSI.
• An application can request multicasting and other protocol services not supported by Winsock 1.1.
• It offers access to multiple name spaces.
• It offers an application the possibility of choosing services based on cost.

Xmodem is an error-correcting protocol for modems that was created in 1978 by Ward Christensen and became a de facto standard. Modems that agree on using the Xmodem protocol send data in 128-byte blocks. If a block is received successfully, a positive (ACK) acknowledgement is returned. If an error is detected, a negative (NAK) acknowledgement is returned and the block is resent. Xmodem uses the checksum method of error checking.
 
 

Xon/Xoff (sometimes written "X-on/X-off" or "XON/XOFF" and pronounced eks-AWN eks-AWF) is a protocol for controlling the flow of data between computers and other devices on an asynchronous serial connection. For example, a computer typically sends data to a printer faster than the printer can print. The printer contains a buffer where data is stored until the printer catches up with the computer. If the buffer becomes full before the printer catches up, a small microprocessor in the printer sends back an X/off signal to stop sending data. When enough data is printed and buffer storage becomes free, the printer sends an X/on signal telling the computer to resume sending data.

The "X" stands for "transmitter" so the X/on and X/off are signals to turn a transmitter on or off. The actual signal for X/on is the same bit configuration as the ASCII Ctrl-Q keyboard combination. The X/off signal is the Ctrl-S character.

When you define your modem to your computer's operating system, you may need to specify the use of flow control with X/on/Xoff or with CTS/RTS (Clear to Send/Ready to Send). When sending binary data, Xon/Xoff may not be recognized because it is character-encoded.
 
 

The X.25 protocol, adopted as a standard by the Consultative Committee for International Telegraph and Telephone (CCITT), is a commonly-used network protocol. The X.25 protocol allows computers on different public networks (such as CompuServe, Tymnet, or a TCP/IP network) to communicate through an intermediary computer at the network layer level. X.25's protocols correspond closely to the data-link and physical-layer protocols defined in the Open Systems Interconnection (OSI) communication model.
 
 

A ZIF (Zero Insertion Force) socket is the physical way that Intel's 486 and Pentium microprocessors up to Pentium II connect on the computer motherboard to the data bus. As its name implies, the ZIF socket is designed for ease of manufacture and so that the average computer owner will be able to upgrade the microprocessor. The ZIF socket contains a lever that opens and closes, securing the microprocessor in place.

The ZIF interface evolved through eight variations, each with a differing number of pins and pin layout arrangements. Currently, the best-known is Socket 7, the configuration used in the Pentium microprocessor. (However, the Pentium Pro uses Socket 8.) With the Pentium II microprocessor, which is based on Intel's new P6 micro architecture, Intel has changed to a new connection configuration called Slot 1 and Slot 2. In this configuration, the microprocessor comes packaged in a cartridge that fits into a 242-contact or 330-contact slot in the motherboard.

AMD and Cyrix, which offer competitive processors, continue to use the Socket 7 arrangement.

The following table summarizes the Zero Insertion Force (ZIF) socket characteristics for different Intel processors.

Zmodem is an error-correcting protocol for modems. Modems that agree on using the Zmodem protocol send data in 512-byte blocks. If a block arrives and an error is detected, a "NAK" (negative acknowledgement) is returned and the block is resent.
 
 

The Zoomed Video port (ZV port) is a technology that supports the delivery of full-screen motion video and multimedia to notebook computers. The ZV port allows special software and a version of the PC Card called a ZV Port Card to provide a separate dedicated, point-to-point bus or path from continuously arriving video signals directly to the display controller so that they do not need to be handled by the main bus or the CPU. ZV ports are provided in IBM, Toshiba, and other manufacturers' notebook computers.

With the ZV port technology, video signals are sent in compressed files using the MPEG standard. The ZV Port Card decompresses the files and sends the data directly to the video frame buffer managed by the display controller. The technology can also be used for capturing images sent to the display from a video camera and storing them on a hard disk. Combining user input from the computer's regular PCI bus with the video from the ZV port, notebook users can play interactive MPEG-based games.

The specification for the ZV port is an industry standard sponsored by the PCMCIA.