Bandwidth
Bandwidth refers to the amount of data a cable can carry; measured in bits per second (bps) for digital signals, or in hertz (Hz) for analog signals such as sound waves. An analog bandwidth is computed by subtracting the lower frequency from the higher one. For example, the bandwidth of the human voice is roughly 2,700 Hz (3,000 - 300). A larger bandwidth means greater potential data-transmission capability. For digital signals, a higher bit rate represents a larger bandwidth. However, the higher the frequency,
the shorter the wavelength. A higher bandwidth (that is, a higher signal frequency) means faster transmission, which means a shorter signal. With a short signal, there is a smaller margin for error in interpreting the signal. This means that the effects of attenuation and other signal distortion must be kept to a minimum. A signal traveling along a cable degrades with distance. It is possible to connect the cable to special components that can clean up and rejuvenate a signal. High-frequency electrical signals must be cleaned up

BIOS (Basic Input/Output System)
The BIOS is a collection of services on a ROM (read-only memory) chip. The BIOS services enable hardware and software, operating systems and applications, and also applications and users to communicate with each other. The BIOS services are loaded automatically into specific addresses and should always be accessible. BIOS services are updated and expanded to handle newer devices and greater demands. To get a newer BIOS, you simply need to replace the ROM chip in your computer with an appropriate upgrade chip.

Bit
A binary digit is the smallest unit of information. A bit can have a value of 0 or 1 in a digital system. All but the low-level protocols move information in larger chunks, such as bytes, which consists of multiple bits.

Bookmark
In gopher environments on the Internet, a bookmark is used to mark a specific menu or directory on a gopher server. Once the bookmark has been created and placed at the desired location, it’s possible to get almost immediate access to that location, rather than having to work your way through layers of menus.

Broadcast
To simultaneously send the same message to multiple recipients. Broadcasting is a useful feature in e-mail systems. It is also supported by some fax systems. In networking, a distinction is made between broadcasting and multicasting. Broadcasting sends a message to everyone on the network whereas multicasting sends a message to a select list of recipients.

Byte
A collection of, usually eight, bits (but rarely worth a dollar anymore). A byte generally represents a character or digit.

CD-ROM Drive
CD-ROM stands for compact disc, read-only memory. A CD-ROM drive is a peripheral device for reading CDs, which have a huge capacity (660 megabytes).

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

COM1, COM2, COMx
On a PC, the names associated with successive serial ports. Devices that might be connected to such a port include modems, pointer devices, and some printers.

Connectivity
A computer buzzword that refers to a program or device's ability to link with other programs and devices. For example, a program that can import data from a wide variety of other programs and can export data in many different formats is said to have good connectivity. On the other hand, computers that have difficulty linking into a network (many laptop computers, for example) have poor connectivity.

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

CPU (Central Processing Unit)
The main processor in a computer. The CPU may be aided in its work by special-purpose chips, such as graphics accelerators and the UART (universal asynchronous receiver/transmitter).

CSU (Channel Service Unit)
A CSU is part of the integrated services unit (ISU) component that replaces a modem on a digital line. The CSU is mainly responsible for making the signals well-behaved and protecting the public carrier’s lines from a malfunctioning data service unit (DSU). In particular, a CSU prevents faulty customer-premises equipment (CPE), such as DSUs, from affecting a public carrier’s transmission systems and ensures that all signals placed on the line are appropriately timed and formed. All CSU designs must be approved and certified by the FCC (Federal Communications Commission).

Database
A database is an indexed collection of information. The index imposes an order on the information and also provides access to the information in the database. The information in a database can be accessed, modified, or retrieved using a query language. The most widely used query language is SQL (Structured Query Language), which forms the basis for most other query languages currently in use.

Dial-up Line
A dial-up line is a nondedicated communications line in which a connection can be established by dialing the number, or code, associated with the destination. A common example of a dial-up line, also called a switched line or public line, is the public telephone line. Dial-up lines generally support speeds of 2,400 to 9,600 bps. The connection is created at dial-up time, and it is destroyed when the call is finished. This is in contrast to a leased line (also called a private or dedicated line), in which a connection between two specific points is always available. With a dial-up line, the same calling node can be connected with an arbitrary number of destinations. Costs accrue only for the duration of a particular connection.

DNS (Domain Naming System)
DNS is the distributed naming service used on the Internet. The DNS can provide a machine’s IP address, given domain names for the machine. Various products have been developed to provide DNS, such as the Berkeley Internet Name Domain (BIND). DNS is described in RFCs 1101, 1183, and 1637.

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

Download
To transfer data, such as a file, from a host computer to a remote machine. For example, the host may be a mainframe or a BBS (bulletin board system) computer. Downloading requires a communications protocol that both the host and recipient can under-stand and use.

Drive
A drive is a data storage location. Drives may be the following:

These use physical resources to mimic physical drives, but their con-tents disappear when the computer is turned off. In the DOS environment, drives are referenced by letters. For example, A: and B: represent floppy disk drives on a PC. In a NetWare network, drives A: through E: rep-resent local drives on a workstation; drives F:, G:, and so on, are logical network drives.

DSL (Digital Subscriber Lines)
Refers collectively to all types of digital subscriber lines, the two main categories being ADSL and SDSL. Two other types of xDSL technologies are High-data-rate DSL (HDSL) and Single-line DSL (SDSL).  DSL technologies use sophisticated modulation schemes to pack data onto copper wires. They are sometimes referred to as last-mile technologies because they are used only for connections from a telephone switching station to a home or office, not between switching stations.
xDSL is similar to ISDN inasmuch as both operate over existing copper telephone lines (POTS) and both require the short runs to a central telephone office (usually less than 20,000 feet). However, xDSL offers much higher speeds - up to 32 Mbps for downstream traffic, and from 32 Kbps to over 1 Mbps for upstream traffic.

DSS (Digital Satellite System)
A network of satellites that broadcast digital data. An example of a DSS is DirecTV, which broadcasts digital television signals. DSS's are expected to become more important as the TV and computer converge into a single medium for information and entertainment.

DSU/CSU (Data Service Unit/Channel Service Unit)
In digital telecommunications, the DSU and CSU are two components of a DCE (Data-Communications Equipment) device. These components provide access to digital services over DDS, T1, and other types of lines.

E-Mail (Electronic Mail)
E-mail (also written as email) is an application that provides a message transfer and storage service for the nodes on a network or internetwork or for a stand-alone machine through a dial-up service. Each user has an electronic mailbox (a unique directory for storing electronic mail), and other users can send e-mail messages to the user at this mailbox. The e-mail messages are sent to an e-mail address. For the end-user, an e-mail address is generally written as a sequence of names, separated by periods or other special characters, as in fiddle@faddle.edu.
Once the message is stored in the recipient’s mailbox, the owner of the mailbox can retrieve whatever messages look important and/or interesting. E-mail packages differ in the ease with which such selections can be made and also in the services the packages provide.

ESDI (Enhanced Small Device Interface)
An interface and storage format for hard disks. ESDI can support relatively high-capacity (up to a gigabyte or so) drives and supports access times as low as about 20 milliseconds.

Ethernet
Ethernet is shared-media network architecture. Its elements are the result of work by Xerox, Intel, and Digital Equipment Corporation. Ethernet, along with variants defined in the IEEE 802.3 standard, is currently the most widely used architecture for local-area networks (LANs). According to some estimates, there are more than 10 million Ethernet nodes around the world. Estimates of Ethernet’s share of the LAN configurations range between 60 and 90 percent.

Expansion Bus
A set of slots, such as those on a mother-board, into which expansion cards can be plugged in order to provide the computer with additional capabilities and access to external devices.

Firewall
A firewall is a network component that pro-vides a security barrier between networks or network segments. Firewalls are generally set up to protect a particular network or net-work component from attack, or unauthorized penetration, by outside invaders. However, a firewall also may be set up to protect vital corporate or institutional data or resources from internal attacks or incompetence. Internal firewalls are generally placed between administrative, or security, domains in a corporate or institutional network. For example, a firewall might be set up between the network domain that houses the payroll and personnel information and other parts of the corporate network.

Fractional T1
In digital communications, a portion of a 1.544 megabit per second T1 carrier, or line. Fractional T1 lines are available from IXCs (interexchange carriers) and can have band-widths of 384, 512, or 768 kilobits per second, corresponding roughly to a quarter, a third, and half of a full T1 carrier.

Frame Relay
A packet-switching protocol for connecting devices on a Wide Area Network (WAN). Frame Relay networks in the U.S. support data transfer rates at T-1 (1.544 Mbps) and T-3 (45 Mbps) speeds. In fact, you can think of Frame Relay as a way of utilizing existing T-1 and T-3 lines owned by a service provider. Most telephone companies now provide Frame Relay service for customers who want connections at 56 Kbps to T-1 speeds. (In Europe, Frame Relay speeds vary from 64 Kbps to 2 Mbps. In the U.S., Frame Relay is quite popular because it is relatively inexpensive. However, it is being replaced in some areas by faster technologies, such as ATM.

Full Duplex
A communication setup in which transmissions can go in both directions at the same time. This is in contrast to simplex and half-duplex connections.

GUI (Graphical User Interface)
A graphically based interface, such as Microsoft Windows, Motif, or Macintosh. In GUIs (pronounced "gooeys"), information and commands are presented through icons, and the user gives commands by pointing to or manipulating the icons. GUIs are in contrast to character-based interfaces, such as the default interfaces for DOS or UNIX.

Hard Disk
A hard disk is a magnetic storage device consisting of multiple spinning platters (disks), each with its own read/write heads. Hard disk drives have a much higher storage capacity (up to a gigabyte or more) than floppy disks. They also have a much faster access time and higher transfer rate than floppy disk drives. The access times of hard disks are as low as 5 to 20 milliseconds (ms); floppy disk access times are 200 msec or more. Hard disks differ from each other (and from floppy disk drives) in the interfaces and formats encoding techniques and rules) used. 

Half Duplex
A communication setup in which transmissions can go in either direction, but in only one direction at a time. With half-duplex operation, the entire bandwidth can be used for the transmission. In contrast, full-duplex operation must split the bandwidth between the two directions.

Home Page
A home page is the starting point for a hypertext document on the World Wide Web (WWW). The links from a home page may lead to other documents at the same site or to documents that belong to other people or corporations, and that may be scattered around the world. These linked Web pages may themselves be home pages. Each home page is associated with a URL (Uniform Resource Locator), which specifies the page’s location. For example, the following URL gets you to the home page for information about the best Web services—as determined by user votes—in various categories.

HTML (HyperText Markup Language)
HTML is the language used to create hypertext documents for the World Wide Web (WWW). HTML is a markup language, which means that formatting commands, or tags, are written directly into the source file. Tags are interspersed with ordinary text, and are not interpreted until the file is displayed or printed by a browser program. HTML files have two main components: a head and a body.

Hub
A hub is a component that serves as a common termination point for multiple nodes and that can relay signals along the appropriate paths. Generally, a hub is a box with a number of connectors to which nodes are attached, as shown in the figure "A stand-alone hub." Hubs usually accommodate four or eight nodes, and many hubs include connectors for linking to other hubs.

IDE (Intelligent Drive Electronics or Integrated Drive Electronics)
An IDE interface is an interface for mass storage devices, in which the controller is integrated into the disk or CD-ROM drive. Although it really refers to a general technology, most people use the term to refer the ATA specification, which uses this technology. Refer to ATA for more information.

Integrated Software
Software in which several applications are mutually accessible and able to exchange and update data in a consistent and transparent manner. While it is not required, the component applications are generally on a single machine—either a stand-alone computer or on a server. Arguably, office suites (such as Microsoft Office, Novell Perfect-Office, and Lotus SmartSuite) are among the best known and most widely used examples of integrated software. Usually, these components can also be configured to launch other Windows applications.

Internet
A global network connecting millions computers. As of 1998, the Internet has more than 100 million users worldwide, and that number is growing rapidly. More than 100 countries are linked into exchanges of data, news and opinions. Unlike online services, which are centrally controlled, the Internet is decentralized by design. Each Internet computer, called a host, is independent. Its operators can choose which Internet services to use and which local services to make available to the global Internet community. Remarkably, this anarchy by design works exceedingly well.
There are a variety of ways to access the Internet. Most online services, such as America Online, offer access to some Internet services. It is also possible to gain access through a commercial Internet Service Provider (ISP).

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

IP (Internet Protocol) Address
An IP address is an address for a station or other device on the Internet. This type of address consists of 4 bytes, which are represented as decimal values separated by periods, as in 123.45.67.89. In order to ensure uniqueness, IP addresses are assigned in part by the Internet Assigned Numbers Authority (IANA).

ISDN (Integrated Services Digital Network)
ISDN is a potential telecommunications standard that is capable of sending digitally encoded voice, data, video, and other signals on the same lines. ISDN can also provide access to a variety of communications, information processing, and supplementary services. The figure "Context and properties of ISDN" summarizes the characteristics of ISDN. ISDN is a completely digital service. An ISDN implementation must provide any adapters needed to translate analog or non-ISDN compatible signals.

Jumper
A wire or metal bridge whose placement can be used to close a circuit. A jumper can establish electrical connections that indicate configuration settings. Jumpers are alternatives to DIP switches for storing configuration values. A group of jumpers is called a jumper block.

Line Speed
In telephony, line speed refers to the transmission speed a line will support for a given grade of service (GoS).

Log On
To make a computer system or network recognizes you so that you can begin a computer session. Most personal computers have no log-on procedure -- you just turn the machine on and begin working. For larger systems and networks, however, you usually need to enter a username and password before the computer system will allow you to execute programs. Alternative spellings for log on are log in and login.

Log Out
To end a session at the computer. For personal computers, you can log out simply by exiting applications and turning the machine off. On larger computers and networks, where you share computer resources with other users, there is generally an operating system command that lets you log off.

LPT1
The logical name for the primary parallel port. Additional parallel ports are LPT2 and LPT3. As a device, this port is also known as PRN.

MAN (Metropolitan-Area Network)
A MAN is a network with a maximum range of about 75 kilometers (45 miles) or so, and with high-speed transmission capabilities. Most MANs includes some type of telecommunications components and activity to handle long-distance transmissions. Because the distances are generally short enough to incur minimal telecommunications costs, the connections usually use very high-speed lines, such as T3, at almost 45 megabits per second (Mbps).

Memory
Internal storage areas in the computer. The term memory identifies data storage that comes in the form of chips, and the word storage is used for memory that exists on tapes or disks. Moreover, the term memory is usually used as shorthand for physical memory, which refers to the actual chips capable of holding data. Some computers also use virtual memory, which expands physical memory onto a hard disk.
Every computer comes with a certain amount of physical memory, usually referred to as main memory or RAM. You can think of main memory as an array of boxes, each of which can hold a single byte of information. A computer that has 1 megabyte of memory, therefore, can hold about 1 million bytes (or characters) of information.

MODEM (MOdulator-DEModulator)
A modem is a device or program that enables a computer to transmit data over telephone lines. Computer information is stored digitally, whereas information transmitted over telephone lines is transmitted in the form of analog waves. A modem converts between these two forms.

Motherboard
The main circuit board in a computer. This board will hold the CPU (central processing unit) and may include a math coprocessor, various other controller chips, and RAM chips. In its role as a backplane, the motherboard provides slots for expansion.

Netscape Navigator
Navigator, from Netscape Communications, is arguably the most widely used graphics-based browser (hypertext reader). The program was designed and co-written by Marc Andreessen—the leader of the team that created the NCSA Mosaic browser. While it can claim Mosaic as an inspiration, Navigator was designed from scratch to improve on, and add features not available in, the NCSA version of that browser.

NetWare
NetWare is a network operating system (NOS) from Novell. Several different versions of NetWare are currently (or have been) available. These versions differ in the hardware they support, in the networking services they provide, and in special features (such as fault tolerance).

Network
A group of two or more computer systems linked together.

Network Station
A machine that is linked to a network. The network station can be either a workstation or a server.

Newsgroup
On the Internet, a newsgroup is any of the 14,500 (and counting) article (posting, or message) collections that have been created. These collections are named and organized by topic, then subtopic, and so forth. Seven of the top-level groupings are carried over the Usenet; other newsgroups fall into the alt category or into any of the several dozen special interest categories. See the "News" article for more details and specific examples. News servers may carry and distribute some or all of the available newsgroups.

NIC (Network Interface Card)
The NIC is the network component with a thousand names, including LAN adapter, LAN card, NIU (network interface unit), network adapter, and network board. An NIC enables a PC to connect to and access a network. The NIC communicates through drivers with the node’s networking software (shell or operating system) at one end, and with the network (the cabling to the other nodes) at the other end. NICs usually fit into expansion slots in a PC.

Node
On a network, a node is simply an element with a network interface card (NIC) installed. A node is generally a computer (a workstation or a server), but may be another type of device, such as a printer or modem. Nodes that are not computers may have an NIC preinstalled.

Operating System
The most important program that runs on a computer. Every general-purpose computer must have an operating system to run other programs. Operating systems perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices such as disk drives and printers.

OS/2
An operating system for PCs developed originally by Microsoft Corporation and IBM, but sold and managed solely by IBM. OS/2 is compatible with DOS and Windows, which means that it can run all DOS and Windows programs. However, programs written specifically to run under OS/2 will not run under DOS or Windows.

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

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

• Type I cards can be up to 3.3 mm thick, and are used primarily for adding additional ROM or RAM to a computer.
• Type II cards can be up to 5.5 mm thick. These cards are often used for modem and fax modem cards.
• Type III cards can be up to 10.5 mm thick, which is sufficiently large for portable disk drives.

Peripheral Device
Any external device attached to a computer. Examples of peripherals include printers, disk drives, display monitors, keyboards, and mice.

PING (Packet Internet Groper)
A utility to determine whether a specific IP address is accessible. It works by sending a packet to the specified address and waiting for a reply. PING is used primarily to troubleshoot Internet connections.

PPTP
Short for Point-to-Point Tunneling Protocol, a new technology for creating Virtual Private Networks (VPNs), developed jointly by Microsoft Corporation, U.S. Robotics, and several remote access vendor companies, known collectively as the PPTP Forum. A VPN is a private network of computers that uses the public Internet to connect some nodes. Because the Internet is essentially an open network, the Point-to-Point Tunneling Protocol (PPTP) is used to ensure that messages transmitted from one VPN node to another are secure. With PPTP, users can dial in to their corporate network via the Internet.
Although PPTP has been submitted to the IETF for standardization, it is currently available only on networks served by a Windows NT 4.0 server and Linux.

Queue
In data handling, a temporary holding structure in which values can be stored until needed. A queue is organized in such a way that the first item added to the queue is also the first item out of the queue. This processing is known as FIFO, for first-in, first-out. Job and print queues are perhaps the best known for those who work with computers.

• Level 0: Provides data striping (spreading out blocks of each file across multiple disks) but no redundancy. This improves performance but does not deliver fault tolerance.

• Level 1: Provides disk mirroring.

• Level 3: Same as Level 0, but also reserves one dedicated disk for error correction data. It provides good performance and some level of fault tolerance.

• Level 5: Provides data striping at the byte level and also stripe error correction information. This results in excellent performance and good fault tolerance. 

RAM (Random Access Memory)
RAM is chip-based working memory, which is the memory used by programs and drivers to execute instructions and to hold data temporarily. RAM chips are distinguished by their access speed, which is on the order of about 70 nanoseconds, and by their capacity, which is currently between 1 and 4 megabytes MB) per chip set. Various types of RAM are distinguished in the literature:

• DRAM (dynamic RAM), which must be refreshed periodically in order to retain its information. Refresh periods are every few milliseconds or so.
• SRAM (static RAM), which retains its contents as long as power is supplied.
• VRAM (video RAM), which is used to provide memory for graphics processing or temporary image storage.

Remote Access
The ability to log onto a network from a distant location. Generally, this implies a computer, a modem, and some remote access software to connect to the network. Whereas remote control refers to taking control of another computer, remote access means that the remote computer actually becomes a full-fledged host on the network. The remote access software dials in directly to the network server. The only difference between a remote host and workstations connected directly to the network is slower data transfer speeds.

ROM (Read Only Memory)
ROM is chip-based memory whose contents can be executed and read, but cannot be changed. Programs are put into ROM in order to save storage and working memory. Many notebook and special-purpose computers have operating systems and special applications in ROM. Diskless workstations have a ROM chip that enables the workstation to boot from a network server.
The following types of ROM are distinguished in the literature:

• EEPROM (electronically erasable, programmable ROM), which allows old data to be erased simply by writing over it
• EPROM (erasable, programmable ROM), which allows old data to be erased by shining UV (ultraviolet) light on the chip in order to "deprogram" it
• PROM (programmable ROM), which can be programmed once, even by the user, but cannot be changed once programmed
• MROM (mask ROM), which is programmed during the manufacturing process and cannot be modified or reprogrammed.

Router
The function of a router is to provide a path from a node on one network to a node on another network. The two networks may be separated by several intervening networks and, possibly, by many miles. The figure "Routers connect nodes on different networks" shows an example of networks with routers. The router provides the path by first determining a route and then providing the initial connection for the path.

Routing
In internetworking, the process of moving a packet of data from source to destination. Routing is usually performed by a dedicated device called a router. Routing is a key feature of the Internet because it enables messages to pass from one computer to another and eventually reach the target machine. Each intermediary computer performs routing by passing along the message to the next computer. Part of this process involves analyzing a routing table to determine the best path.

T1
A dedicated phone connection supporting data rates of 1.544Mbits per second. A T-1 line actually consists of 24 individual channels, each of which supports 64Kbits per second. Each 64Kbit/second channel can be configured to carry voice or data traffic. Most telephone companies allow you to buy just some of these individual channels, known as fractional T-1 access.
T-1 lines are a popular leased line option for businesses connecting to the Internet and for Internet Service Providers (ISPs) connecting to the Internet backbone. The Internet backbone itself consists of faster T-3 connections. T-1 lines are sometimes referred to as DS1 lines.

TCP/IP (Transmission Control Protocol/Internet Protocol)
The suite of communications protocols used to connect hosts on the Internet. TCP/IP uses several protocols, the two main ones being TCP and IP. TCP/IP is built into the UNIX operating system and is used by the Internet, making it the de facto standard for transmitting data over networks. Even network operating systems that have their own protocols, such as Netware, also support TCP/IP.

Trojan Horse
A program that looks harmless but that contains hidden instructions to destroy files, programs, or File Allocation Tables (FATs). The instructions may be “time bombs”, which are triggered by certain dates, times, or user commands.

Tunneling
Tunneling is a method for avoiding protocol restrictions by wrapping packets from one protocol in a packet for another and then transmitting this wrapped, or encapsulated, packet over a network that supports the wrapper protocol.

UNIX
Pronounced yoo-niks, a popular multi-user, multitasking operating system developed at Bell Labs in the early 1970s. Created by just a handful of programmers, UNIX was designed to be a small, flexible system used exclusively by programmers. Although it has matured considerably over the years, UNIX still betrays its origins by its cryptic command names and its general lack of user-friendliness. This is changing, however, with graphical user interfaces such as MOTIF.
UNIX was one of the first operating systems to be written in a high-level programming language, namely C. This meant that it could installed on virtually any computer for which a C compiler existed. This natural portability combined with its low price made it a popular choice among universities. (It was inexpensive because antitrust regulations prohibited Bell Labs from marketing it as a full-scale product.)
Bell Labs distributed the operating system in its source language form, so anyone who obtained a copy could modify and customize it for his own purposes. By the end of the 1970s, dozens of different versions of UNIX were running at various sites.
After its breakup in 1982, AT&T began to market UNIX in earnest. It also began the long and difficult process of defining a standard version of UNIX. To date, there are two main dialects of UNIX; one produced by AT&T known as System V and one developed at Berkeley University and known as BSD4.x, x being a number from 1 to 3.
Due to its portability, flexibility, and power, UNIX has become the leading operating system for workstations. Historically, it has been less popular in the personal computer market, but the emergence of a new version called Linux is revitalizing UNIX across all platforms.

Upload
To transfer data (such as a file) from a PC or other machine to a host machine. For example, the target machine may be a main-frame or a bulletin board system (BBS) computer. In general, an upload transfers from a remote machine to a central one. This process requires a communications protocol that both host and recipient can understand and use.

UPS (Uninterruptible Power Supply)
A UPS is an emergency power source that can deliver a limited amount of power to a file server or other device in the event of a blackout (total loss of power). UPSs are sometimes known as online UPSs to distinguish them from SPSs (standby power supplies), which are also known as offline UPSs. An SPS is similar, but not identical, to a UPS. The main difference is that a UPS always supplies power through a battery, whereas an SPS does so only when there is a power failure.

URL (Uniform Resource Locator)
URL is the global address of documents and other resources on the World Wide Web.
The first part of the address indicates what protocol to use, and the second part specifies the IP address or the domain name where the resource is located.
For example, the two URLs below point to two different files at the domain pcwebopedia.com. The first specifies an executable file that should be fetched using the FTP protocol; the second specifies a Web page that should be fetched using the HTTP protocol.

USB (Universal Serial Bus)
A new external bus standard that supports data transfer rates of 12 Mbps (12 million bits per second). A single USB port can be used to connect up to 127 peripheral devices, such as mice, modems, and keyboards. USB also supports Plug-and-Play installation and hot plugging.
Starting in 1996, a few computer manufacturers started including USB support in their new machines. It wasn't until the release of the best-selling iMac in 1998 that USB become widespread. It is expected to eventually completely replace serial and parallel ports.

Workstation
A type of computer used for engineering applications (CAD/CAM), desktop publishing, software development, and other types of applications that require a moderate amount of computing power and relatively high quality graphics capabilities.
Workstations generally come with a large, high-resolution graphics screen, at least 64 MB (megabytes) of RAM, built-in network support, and a graphical user interface. Most workstations also have a mass storage device such as a disk drive, but a special type of workstation, called a diskless workstation, comes without a disk drive. The most common operating systems for workstations are UNIX and Windows NT.
In terms of computing power, workstations lie between personal computers and minicomputers, although the line is fuzzy on both ends. High-end personal computers are equivalent to low-end workstations. And high-end workstations are equivalent to minicomputers.
Like personal computers, most workstations are single-user computers. However, workstations are typically linked together to form a local-area network, although they can also be used as stand-alone systems.
The leading manufacturers of workstations are Sun Microsystems, Hewlett-Packard Company, Silicon Graphics Incorporated, and Compaq.
In networking, workstation refers to any computer connected to a local-area network. It could be a workstation or a personal computer.

World Wide Web
A system of Internet servers that support specially formatted documents. The documents are formatted in a language called HTML (HyperText Markup Language) that supports links to other documents, as well as graphics, audio, and video files. This means you can jump from one document to another simply by clicking on hot spots. Not all Internet servers are part of the World Wide Web.
There are several applications called Web browsers that make it easy to access the World Wide Web, two of the most popular being Netscape Navigator and Microsoft's Internet Explorer.