Return to List of Terms

QAM
Quadrature Amplitude Modulation, is a method of combining two amplitude-modulated signals into a single channel, thereby doubling the effective bandwidth. QAM is used with pulse amplitude modulation (PAM) in digital systems, especially in wireless applications.

QoS
Quality of Service.

QPS
Queries-per-second is a measure of how much traffic a particular query server is handling at a given time. On the Internet, the activity in the collection of servers that serve as the domain name system is sometimes measured in queries-per-second.

QXGA
Quantum Extended Graphics Array, a display specification that is capable of supporting 2048 x 1536 resolution.

RAD
Rapid Application Development, is a programming system that enables one to quickly build working programs. RAD systems provide a number of tools to help build GUIs. Examples of popular RAD systems are Visual Basic and Delphi.

Radio Button
This is a way of selecting a choice in a list of options. Normally only one option from the list can be selected at any one time.

RADIUS
Remote Authentication Dial-In User Service, an authentication and accounting system used by many ISPs. When you dial in to the ISP you must enter your username and password. This information is passed to a RADIUS server, which checks that the information is correct, and then authorizes access to the ISP system. Though not an official standard, the RADIUS specification is maintained by a working group of the IETF.

Rain Fade
Rain fade is an interruption of wireless communication signals as a result of rain or snow droplets whose separation approximates the signal wavelengths. The phenomenon can affect satellite Internet connections as well as satellite television and other systems.

RAM
Random Access Memory. Hardware inside your computer that stores data extremely quickly, but on a non-permanent basis. Data must be written to a persistent storage device such as a hard disk to keep it long term.

RARP
Reverse Address Resolution Protocol, a TCP/IP protocol that permits a physical address, such as an Ethernet address, to be translated into an address. Hosts such as diskless workstations often only know their hardware interface addresses, or MAC address, when booted but not their IP addresses. They must discover their IP addresses from an external source, usually a RARP server. RARP is defined in RFC 903.

RAS
(1) Remote Access Server. A server that is dedicated to handling users that are not on a LAN but need remote access to it. The remote access server allows users to gain access to files and print services on the LAN from a remote location. For example, a user who dials into a network from home using an analog modem or an ISDN connection will dial into a remote access server. Once the user is authenticated he can access shared drives and printers as if he were physically connected to the office LAN.

(2) Remote Access Service. A feature built into Windows NT that enables users to log into an NT-based LAN using a modem, X.25 connection or WAN link. RAS works with several major network protocols, including TCP/IP, IPX, and Netbeui. To use RAS from a remote node, you need a RAS client program, which is built into most versions of Windows, or any PPP client software. For example, most remote control programs work with RAS.

(3) Row Address Strobe. A signal, or strobe, sent by the processor to a DRAM circuit to activate a row address. DRAM stores data in a series of rows and columns, similar in theory to a spreadsheet, and each cell where a data bit is stored exists in both a row and a column. A processor uses RAS and CAS signals to retrieve data from DRAM.

Raster Graphics
Also referred to as bitmaps, they are defined by pixel by pixel. Typically known formats are GIF, TIFF and JPEG.

RBAC
Role-Based Access Control, a system of controlling which users have access to resources based on the role of the user.

RCDD
Registered Communications Distribution Designer.

RDBMS
Relational DataBase Management System. A type of database management system (DBMS) that stores data in the form of related table. Relational databases are powerful because they require few assumptions about how data is related or how it will be extracted from the database. As a result, the same database can be viewed in many different ways. An important feature of relational system is that a single database can be spread across several tables. This differs from flat-file databases, in which each database is self-contained in a single table. Almost all full-scale database systems are RDBMS's. Small database systems, however, use other designs that provide less flexibility in posing queries.

RDP
Remote Desktop Protocol.

RDRAM
Rambus DRAM, a type of memory (DRAM) developed by Rambus, Inc. Whereas the fastest current memory technologies used by PCs (SDRAM) can deliver data at a maximum speed of about 100MHz, RDRAM transfers data at up to 800 MHz. In 1997, Intel announced that it would license the Rambus technology for use on its future motherboards, thus making it the likely de facto standard for memory architectures. However, a consortium of computer vendors is working on an alternative memory architecture called SyncLink DRAM (SLDRAM). RDRAM is already being used in place of VRAM in some graphics accelerator boards . As of late 1999, Intel has been using RDRAM in its Pentium III Xeon processors and more recently in its Pentium 4 processors. Intel and Rambus are also working a new version of RDRAM, called nDRAM, that will support data transfer speeds at up to 1,600 MHz.

Reciprocol Link
A hyperlink placed on a Website in return for another site having put a link on its page.

Re-Mailer
Also known as an e-mail reflector. A sender's e-mail is kept anonymous and is commonly known as anonymous e-mail.

Repeater
A network device used to regenerate or replicate a signal. Repeaters are used in transmission systems to regenerate analog or digital signals distorted by transmission loss. A repeater cannot do the intelligent routing performed by bridges and routers.

RFC
Request For Comments, a series of notes about the Internet. An Internet Document can be submitted to the IETF by anyone, but the IETF decides if the document becomes an RFC. Eventually, if it gains enough interest, it may evolve into an Internet standard. Each RFC is designated by an RFC number. Once published, an RFC never changes. Modifications to an original RFC are assigned a new RFC number.

RFID
Radio Frequency IDentification, is a technology that incorporates the use of electromagnetic or electrostatic coupling in the radio frequency portion of the electromagnetic spectrum to uniquely identify an object, animal, or person. RFID is coming into increasing use in industry as an alternative to the bar code. The advantage of RFID is that it does not require direct contact or line-of-sight scanning.

RIMM
A memory module using Rambus technology.  It is used with RDRAM chips. It is similar to a DIMM package but uses different pin settings. Rambus trademarked the term RIMM as an entire word. It is sometimes incorrectly used as an acronym for Rambus Inline Memory Module.

RIP
(1) Raster Image Processor. A hardware - software combination that converts a vector image into a bit-mapped image. All PostScript printers contain a RIP that converts the PostScript command into bit-mapped page that the printer can output.

(2) Regulation of Investigatory Powers ACT. This UK Act is also known as the email snooping Act. It allows the government to tap into ISPs and also allows employers to read employee emails.

(3) Routing Information Protocol. A protocol defined by RFC 1058 that specifies how router exchange routing table information. With RIP, routers periodically exchange entire tables. Because this is inefficient, RIP is gradually being replaced by a newer protocol called OSPF.

RIPE NCC
Réseaux IP Européens Network Coordination Centre. RIPE NCC is one of three regional Internet registries that supply and administer IP addresses. Founded in 1989, RIPE NCC is a non-profit organisation run by volunteers. RIPE NCC provides IP numbers to Europe, the Middle East and parts of Africa and Asia.

RISC
Reduced Instruction Set Computer, a type of microprocessor that recognizes a relatively limited number of instructions.

RMON
Remote monitoring. A network management protocol that allows network information to be gathered at a single workstation. Whereas SNMP gathers network data from a single type of Management Information Base (MIB), RMON 1 defines nine additional MIBs that provide a much richer set of data about network usage. For RMON to work, network devices, such as hub and switches, must be designed to support it. The newest version of RMON, RMON 2, provides data about traffic at the network layer in addition to the physical layer. This allows administrators to analyse traffic by protocol.

Roaming
In wireless networking, roaming refers to the ability to move from one Access Point coverage area to another without interruption in service or loss in connectivity.

ROI
Return On Investment.

ROKSO
Register Of Known Spam Operations, a free-access public register of spam operations that have been thrown off of at least three ISPs for their spamming activities.

ROM
Read-Only Memory, computer memory on which data has been prerecorded. Once data has been written onto a ROM chip, it cannot be removed and can only be read.

Router
A device which connects any number of LANs by routing packets of data appropriately. The invention of the router made internetworking (the internet) possible.

RSVP
Resource Reservation Protocol. A protocol that allows the reservation of routes on the internet, particularly for the transmission of high-bandwidth messages.

RTMP
Routing Table Maintainance Protocol, is a distance vector routing protocol.

RTO
Retransmission TimeOut.

Runt
A packet that is too small to transfer.

SAC
Single-Attached Concentrator. FDDI or CDDI concentrator that connects to the network by being cascaded from the master port of another FDDI or CDDI concentrator.

SAML
Security Assertion Markup Language, an XML-based framework for ensuring that transmitted communications are secure. SAML defines mechanisms to exchange authentication, authorization and nonrepudiation information, allowing single signon capabilities for Web services.

SAN
Storage Area Network is a high-speed subnetwork of shared storage devices that is available to all servers on a LAN or WAN. As the data on a SAN does not reside directly on any of the network servers, increasing the amount of data and/or size of the SAN, the network servers capacity for business applications is not affected.

SASL
Simple Authentication and Security Layer. Originating with RFC2222, SASL is a method for adding authentication support to connection-based protocols. SASL takes effect when a protocol initiates a command for identifying and authenticating a user to a server. SASL also includes an option for negotiating protection of subsequent protocol interactions. With this option in effect, SASL places a security layer between the protocol and the connection.

SAX
Simple API for XML, originally a Java-only API. SAX was the first widely adopted API for XML in Java, and is a “de facto” standard.

SCM
Supply Chain Management.

Screen Saver
A small program that takes over the display screen if there are no keystrokes or mouse movements for a specified duration. Screen savers were originally developed to prevent ghosting, the permanent etching of a pattern on a display screen. For older monochrome monitors, ghosting often occurred if the same pattern was displayed on a display screen for a long period of time. Screen savers would prevent this by either blanking out the screen entirely or by displaying a constantly moving image. Modern display screens do not suffer so much from this ghosting problem.

SCSI
Small Computer System Interface, is a parallel interface standard used by Apple Macintosh computers, PCs, and many UNIX systems for attaching peripheral devices to computers. Nearly all Apple Macintosh computers, excluding only the earliest Macs and the recent iMac, come with a SCSI port for attaching devices such as disk drives and printers.
SCSI interfaces provide for faster data transmission rates (up to 80Mbps) than standard serial and parallel ports . In addition, you can attach many devices to a single SCSI port, so that SCSI is really an I/O bus rather than simply an interface.
Although SCSI is an ANSI standard, there are many variations of it, so two SCSI interfaces may be in compatible.

SDK
Software Development Kit, a programming package that enables a programmer to develop applications for a specific platforms. Typically an SDK includes one or more APIs, programming tools, and documentation.

SDRAM
Synchronous DRAM, a new type of DRAM that can run at much higher clock speeds than conventional memory. SDRAM actually synchronizes itself with the CPU's bus and is capable of running at 133MHz, about three times faster than conventional FPM RAM, and about twice as fast EDO-DRAM and BEDO DRAM. SDRAM is replacing EDO DRAM in many newer computers.
Today's fastest Pentium systems use CPU buses running at 100 MHz, so SDRAM can keep up with them, though barely. Future PCs, however, are expected to have CPU buses running at 200MHz or faster. SDRAM is not expected to support these high speeds which is why new memory technologies, such as RDRAM and SLDRAM, are being developed.

Search Engine
A website that allows you to search for certain topics using keywords and phrases.

Segment
(1) In networks, a section of a network that is bounded by bridges, routers or switches. Dividing an Ethernet into multiple segments is one of the most common ways of increasing available bandwidth on the LAN. If segmented correctly, most network traffic will remain within a single segment, enjoying the full 10 Mbps bandwidth. Hubs and switches are used to connect each segment to the rest of the LAN.

(2) In virtual memory system, a variable-sized portion of data that is swapped in and out of main memory. Contrast with page.

(3) In graphics, a piece of a polyline, which is a fixed-sized portion of data.

SEO
Search Engine Optimisation, the process of increasing the amount of visitors to a Web site by ranking high in the search results of a search engine. The higher a Web site ranks in the results of a search, the greater the chance that that site will be visited by a user. It is common practice for Internet users to not click through pages and pages of search results, so where a site ranks in a search is essential for directing more traffic toward the site. SEO helps to ensure that a site is accessible to a search engine and improves the chances that the site will be found by the search engine. A website that allows you to search for certain topics using keywords and phrases.

Serial ATA
Serial ATA is a disk-interface technology developed by a group of the industry's leading vendors to replace parallel ATA. The Serial ATA 1.0 specification was released in August 2001. Serial ATA is scalable and will allow future enhancements to the computing platform.

Server
A computer that supplies the appropriate data on request from a client, e.g. a computer on the internet serving web pages.

Server Farm
Also referred to as server cluster, computer farm or ranch. A server farm is a group of networked servers that are housed in one location. A server farm streamlines internal processes by distributing the workload between the individual components of the farm and expedites computing processes by harnessing the power of multiple servers. The farms rely on load-balancing software that accomplishes such tasks as tracking demand for processing power from different machines, prioritising the tasks and scheduling and rescheduling them depending on priority and demand that users put on the network.

SET
Secure Electronic Transaction, a standard that will enable secure credit card transactions on the Internet. SET has been endorsed by virtually all the major players in the e-commerce arena.

SGCP
Simple Gateway Control Protocol. Controls Voice over IP gateways by an external call control element.

SGML
Standard Generalized Markup Language, a system for organizing and tagging elements of a document. SGML was developed and standardized by the International Organization for Standards (ISO) in 1986.
SGML itself does not specify any particular formatting; rather, it specifies the rules for tagging elements. These tags can then be interpreted to format elements in different ways.
SGML is used widely to manage large documents that are subject to frequent revisions and need to be printed in different formats. Because it is a large and complex system, it is not yet widely used on personal computers. However, the growth of Internet, and especially the World Wide Web, is creating renewed interest in SGML because the World Wide Web uses HTML, which is one way of defining and interpreting tags according to SGML rules.

SGSN
Serving GPRS Support Node.

Shareware
Software available to download and use for a limited time before deciding to purchase it.

SHTML
A web file suffix denoting that the page being received has been produced on the fly.

SIMM
Single In-line Memory Module, a small circuit board that can hold a group of memory chips. Typically, SIMMs hold up 8 (on Macintoshes ) or 9 (on PCs) RAM chips. On PCs, the ninth chip is often used for parity error checking. Unlike memory chips, SIMMs are measured in bytes rather than bits. SIMMs are easier to install than individual memory chips. The bus from a SIMM to the actual memory chips is 32 bits wide. A newer technology, called dual in-line memory module (DIMM) , provides a 64-bit bus. For modern Pentium microprocessors that have a 64-bit bus, you must use either DIMMs or pairs of SIMMs.

SIMPLE
Session initiation protocol for Instant Messaging and Presence Leveraging Extensions. An application of the SIP protocol for server-to-server and client-to-server interoperability in instant messaging . SIMPLE is a step in bringing standardization to instant messaging.

SIP
(1) Single In-line Package, a type of housing for electronic components in which the connecting pins protrude from one side. A SIP is also called a Single In-line Pin Package (SIPP).

(2) Session Initiated Protocol, or Session Initiation Protocol. A signaling protocol for Internet conferencing, telephony, presence, events notification and instant messaging. The protocol initiates call setup, routing, authentication and other feature messages to endpoints within an IP domain.

SLA
Service Level Agreement.

SLDRAM
SyncLink DRAM, a new type of memory being developed by a consortium of computer manufacturers. SLDRAM is competing with RDRAM as the future PC memory architecture.

SLIP
Serial Line Internet Protocol. A method of connecting to the Internet. Another more common method is PPP. SLIP is an older and simpler protocol, but from a practical perspective, there's not much difference between connecting to the Internet via SLIP or PPP. In general, ISPs offer only one protocol although some support both protocols.

Smartdrive
A disk caching system provided by Microsoft with later versions of DOS and used with Windows 3.1 Disk caching provides faster access to data on a hard disk. Smartdrive allows you to monitor how the cache is used and change the cache size to optimise performance. Starting with Windows 95, Smartdrive was replaced by a disk caching system called VCACHE.

SMB
Server Message Block, a message format used by DOS and Windows to share files, directories and devices.

SMDS
Switched Multimegabit Data Services, a high-speed switched data communications service offered by telephone companies that enable organizations to connect geographically separate LANs into a single WAN. Prior to SMDS's arrival in 1995, the only way to connect LANs was through a dedicated private line. This is still the way most WANs are connected, but SMDS is becoming an increasingly attractive alternative because it is more flexible and in many cases more economical.

SMIS
Storage Management Interface Specification.

SMP
Symmetric Multi-Processors.

SMS
(1) Systems Management Server, a set of tools from Microsoft that assists in managing PC connected to a LAN. SMS enables a network administrator to create an inventory of all the hardware and software on the network and to store it in an SMS database. Using this database, SMS can then perform software distribution and installation over the LAN. SMS also enables a network administrator to perform diagnostic tests on PCs attached to the LAN.

(2) Short Message Service, is the transmission of short text messages to and from a mobile phone, fax machine and/or IP address. Messages must be no longer than 160 alpha-numeric characters and contain no images or graphics. Once a message is sent, it is received by a Short Message Service Center (SMSC), which must then get it to the appropriate mobile device.

SMT
Simultaneous Multi-Threading Technology.

SMTP
Simple Mail Transfer Protocol, a protocol for sending e-mail messages between servers. Most e-mail systems that send mail over the Internet use SMTP to send messages from one server to another; the messages can then be retrieved with an e-mail client using either POP or IMAP.

SNA
Systems Network Architecture. A set of network protocols developed by IBM.

SNAP
SubNetwork Access Protocol. A frame used in Ethernet, Token Ring, and FDDI LANs. The 3 primary functions executed by the frame are data transfer, connection management and quality of service selection.

SNIA
Storage Networking Industry Association.

SNMP
Simple Network Management Protocol, a set of protocols for managing complex network. SNMP works by sending messages, called protocol data units (PDUs), to different parts of a network. SNMP-compliant devices, called agents, store data about themselves in Management Information Bases (MIBs) and return this data to the SNMP requesters.

SO-DIMM
Small Outline DIMM, a small version of a DIMM used commonly in laptops. Whereas a full-size DIMM has 168 pins and supports 64-bit transfers, a SO DIMM has only 72 pins, which supports only 32-bit transfers, or 144 pins, which supports a full 64-bit transfer.

SOA
Service-Oriented Architecture.

SOAP
Simple Object Access Protocol provides a way for applications to communicate with each other over the Internet, independent of platform. Unlike DCOM's IIOP, SOAP piggybacks a DOM onto HTTP (port 80) in order to penetrate server firewalls, which are usually configured to accept port 80 and port 21 (FTP) requests.
SOAP relies on XML to define the format of the information and then adds the necessary HTTP headers to send it.

Socket
(1) A software object that connects an application to a network protocol.

(2) A receptacle into which a plug can be inserted.

(3) A receptacle for a microprocessor or other hardware component.

Software
Computer instructions stored electronically as data. Non-tangible, unlike hardware.

Solar Fade
Solar fade, also called sun interference, is a phenomenon that occurs in satellite communications on certain occasions when the downlink signal is aligned with the sun's position and it is overcome by signal noise from the sun.

SONET
Synchronous Optical Network, is a standard for connecting fiber-optic transmission systems.  It is now an ANSI standard.  The international equivalent of a sonet, is called SDH.

SORBS
Spam & Open Relay Blocking System.

Southbridge
Southbridge is an Intel chipset that manages the basic forms of input/output such as USB, serial, audio, IDE, and ISA I/O in a computer. Southbridge is one of two chipsets that are collectively called Northbridge/Southbridge. Unlike Northbridge, Southbridge consists of one chip, which sits on Northbridge's PCI bus.
See Northbridge .

Spam
Casual name for Unsolicited Bulk Email (UBE). Equivalent to 'junk' mail (can also be used as a verb).

SPARC
Scalable Processor ARChitecture, a RISC technology.

SPEC
(1) Standard Performance Evaluation Corporation, a nonprofit corporation set up by many computer and microprocessor vendors to create a standard set of benchmark tests.

(2) Specification, as in a functional specification.

Spew
Relating to newsgroups and chat rooms. This is when one of the participants repeatedly types, or talks, about the same thing.

SPEWS
Spam Prevention Early Warning System.

Spider
A program that automatically fetches Web pages. Spiders are used to feed pages to search engines. It's called a spider because it crawls over the Web. Another term for these programs is webcrawler. Because most Web pages contain links to other pages, a spider can start almost anywhere. As soon as it sees a link to another page, it goes off and fetches it.

Splash Page
The page of a Web site that the user sees first before being given the option to continue to the main content of the site. Splash pages are used to promote a company, service or product or are used to inform the user of what kind of software or browser is necessary in order to view the rest of the site's pages. Often a splash page will consist of animated graphics and sounds that entice the user into exploring the rest of the Web site. Some splash pages will bring the user to the main Web site automatically, and some require the user to click on a link that will load the main page.
A splash page is sometimes referred to as a splash screen.

SSA
Serial Storage Architecture is IBM's proposed ANSI standard for a standard high speed interface to disk clusters and arrays. It allows full-duplex packet multiplexed serial data transfers at rates of 20Mb/sec in each direction.

SSADM
Structured Systems Analysis and Design Method. It uses a combination of the following:

• Logical Data Modelling
• Data Flow Modelling
• Entity Behaviour Modelling

SSG
Service Selection Gateway. Gateway that offers service providers a means for menu-based service selection. End users can select services from the Dashboard menu.

SSI
(1) Server Side Include.
A type of HTML comment that directs the Web server to dynamically generate data for the Web page whenever it is requested. The simplest comment is #include, which inserts the contents of another file. This is especially useful for ensuring that boilerplate components, such as header and footer, are the same on all pages throughout a Web site. To change a boilerplate element, you need only modify the include file, instead of updating every individual Web page. SSIs can also be used to execute programs and insert the results. They therefore represent a powerful tool for Web developers. Web pages that contain SSIs often end with a .shtml extension, though this is not a requirement. The filename extension enables the Web server to differentiate those pages that need to be processed before they are sent to the browser.

(2) Single System Image.
A form of distributed computing in which by using a common interface multiple networks, distributed databases or servers appear to the user as one system. In other words, the operating system environment is shared by all nodes in the system.

SSL
Secure Sockets Layer, a protocol developed by Netscape for transmitting private documents via the Internet. SSL works by using a public key to encrypt data that's transferred over the SSL connection. Both Netscape Navigator and Internet Explorer support SSL, and many Web sites use the protocol to obtain confidential user information, such as credit card numbers. By convention, URL that require an SSL connection start with https: instead of http:. SSL protocol has been approved by the Internet Engineering Task Force (IETF) as a standard.

SSO
Single SignOn.

SSP
Storage Service Provider, is a company that provides computer storage space and related management services. SSPs also offer periodic backup, archiving and the ability to consolidate data from multiple company locations so that data can be effectively shared.

SSSCA
Security Systems Standards and Certification Act.

STP
(1) Shielded Twisted Pair. 2-pair wiring medium used in a variety of network implementations.

(2) Spanning Tree Protocol. A link management protocol, is part of the IEEE 802.1 standard for media access control bridge. Using the spanning tree algorithm, STP provides pat redundancy while preventing undesirable loops in a network that are created by multiple active paths between stations.

Streaming
A technique for transferring data such that it can be processed as a steady and continuous stream. Streaming technologies are becoming increasingly important with the growth of the Internet because most users do not have fast enough access to download large multimedia files quickly. With streaming, the client browser or plug-in can start displaying the data before the entire file has been transmitted. For streaming to work, the client side receiving the data must be able to collect the data and send it as a steady stream to the application that is processing the data and converting it to sound or pictures.

SWAP
Shared Wireless Access Protocol is a specification for wireless voice and data networking, deveploped by the HomeRF Working Group. It works together with the PSTN network and the Internet through existing telephone and wireless LAN technologies. It supports TDMA for interactive data transfer and CSMA/CA for high-speed packet transfer.

Switch
(1) In networks, a device that filters and forwards packets between LAN segments. Switches operate at the data link layer (layer 2) and sometimes the network layer (layer 3) of the OSI Reference Model and therefore support any packet protocol. LANs that use switches to join segment are called switched LANs or, in the case of Ethernet networks, switched Ethernet LANs.

(2) A small lever or button. The switches on the back of printer and on expansion boards are called DIP switches. A switch that has just two positions is called a toggle switch.

(3) Another word for option or parameter -- a symbol that you add to a command to modify the command's behaviour.

TACACS
Terminal Access Controller Access Control System, an authentication protocol that was commonly used in UNIX networks. TACACS allows a remote access server to communicate with an authentication server in order to determine if the user has access to the network. TACACS is now somewhat dated and is not used as frequently as it once was.

Tag
(n) A command inserted in a document that specifies how the document, or a portion of the document, should be formatted. Tags are used by all format specifications that store documents as text files. This includes SGML and HTML.

(v) To mark a section of a document with a formatting command.

TAN
Tiny Area Network, a LAN with only a few nodes. TANs are typically installed in homes or small office environments so that the devices can share resources, such as modems, files or printers.

TAR
(1) Short for tape archive, a UNIX utility that combines a group of files into a single file. The resulting file has a .tar extension. The tar command does not compress files. Frequently, therefore, a tar file is compressed with the compress or gzip commands to create a file with a .tar.gz or .tar.Z extension. These are comparable to files that have been compressed with PKZIP on a PC platform. Most PC compression utilities, including PKZIP, can open (untar) a tar file.

(2)(v) To combine files with the tar command.

TCB
Trusted Computing Base, refers to the totality of protection mechanisms (hardware, firmware and software) that provide a secure computing environment.

TCG
Trusted Computing Group, is a not-for-profit organisation formed to develop, define, and promote open standards for hardware-enabled trusted computing and security technologies, including hardware building blocks and software interfaces, across multiple platforms, peripherals, and devices.

TCL
Tool Command Language. A powerful interpreter programming language. One of the main strengths of TCL is that it can be easily extended through the addition of custom TCL libraries. It is used for prototyping application as well as for developing CGI scripts, though it is not as popular as PERL for the latter.

TCO
Total Cost of Ownership. Term used to describe the total cost associated with the purchase, administration, and maintenance of a computer and /or network.

TCP/IP
The software used on the internet  to pass information from machine to machine and from network to network. It contains 2 components, Internet Protocol (IP) IP and Transmission Control Protocol (TCP).  It is a routable, flexable, robust, and fault-tolerant protocol that is used by the Internet and most company' internal computer networks.

TCPA
Trusted Computing Platform Alliance.

TCSEC
Trusted Computer System Evaluation Criteria.

TDMA
Time Division Multiple Access is a technology for delivering digital wireless service. It is used by the GSM digital mobile phone system.

TDR
Time-Domain Reflectometer. A tool that sends out a signal and measures how long it takes to return. It is used to find out short and open circuits.

Terabyte
A collection of data totalling 1,024 Gigabytes.

TeX
TeX is a macro processor that provides complete control over typographical formatting.

TFT
Thin Film Transistor. A type of LCD flat-panel display screen, in which each pixel is controlled by from one to four transistor. The TFT technology provides the best resolution of all the flat-panel techniques, but it is also the most expensive. TFT screens are sometimes called active-matrix LCDs.

TFTP
Trivial File Transfer Protocol, a simple form of the File Transfer Protocol (FTP). TFTP uses the User Datagram Protocol (UDP)and provides no security features. It is often used by servers to boot diskless workstations, X-terminals, and routers.

Thread
(1) In online discussions, a series of messages that have been posted as replies to each other. A single forum or conference typically contains many threads covering different subjects. By reading each message in a thread, one after the other, you can see how the discussion has evolved.

(2) In programming, a part of a program that can execute independently of other parts. Operating systems that support multithreading enable programmers to design programs whose threaded parts can execute concurrently.

TIFF
Tagged Image File Format, commonly used graphical format.

TLD
Top-Level Domain, and refers to the suffix attached to Internet domain names. There are a limited number of predefined suffixes, and each one represent a top-level domain. For example .org of www.bcs.org
Current top-level domains include:

• com - commercial businesses; this is the most common TLD
• gov - U.S. government agencies
• edu - Educational institutions such as universities
• org - Organisations (mostly nonprofit)
• mil - Military
• net - Network organisations
• ca - Canada
• cn - China
• th - Thailand
• uk - United Kingdom

TLP
Thread Level Parallelism.

TMDS
(1) Transition Minimised Differential Signalling. A technology used in flat panel, CRTs and projectors, that is a trademark of Silicon Image, Inc.

(2) Trade Marks Directory Service. The leading specialists in trade mark, domain name and company name watching.

TNIEG
Trusted Network Interpretation Environmental Guideline.

Topology
The shape of a LAN or other communications system. Topologies are either physical or logica.
There are four principal topologies used in LANs.
bus topology: All devices are connected to a central cable, called the bus or backbone. Bus networks are relatively inexpensive and easy to install for small networks. Ethernet systems use a bus topology.
ring topology: All devices are connected to one another in the shape of a closed loop, so that each device is connected directly to two other devices, one on either side of it. Ring topologies are relatively expensive and difficult to install, but they offer high bandwidth and can span large distances.
star topology: All devices are connected to a central hub. Star networks are relatively easy to install and manage, but bottlenecks can occur because all data must pass through the hub.
tree topology: A tree topology combines characteristics of linear bus and star topologies. It consists of groups of star-configured workstations connected to a linear bus backbone cable.
These topologies can also be mixed. For example, a bus-star network consists of a high-bandwidth bus, called the backbone, which connects a collections of slower-bandwidth star segments.

TPEP
Trusted Product Evaluation Program.

TPS
Transactions Per Second, a measurement used to determine how many transactions have been processed in one second in transaction-oriented systems.

Traffic
The load on a communications device or system. One of the principal jobs of a system administrator is to monitor traffic levels and take appropriate actions when traffic becomes heavy.

Tree Structure
A type of data structure in which each element is attached to one or more elements directly beneath it. The connections between elements are called branches. Trees are often called inverted trees because they are normally drawn with the root at the top. The elements at the very bottom of an inverted tree (that is, those that have no elements below them) are called leaves. Inverted trees are the data structures used to represent hierarchical file structures. In this case, the leaves are files and the other elements above the leaves are directories. A binary tree is a special type of inverted tree in which each element has only two branches below it.

Trojan Horse
A destructive program that masquerades as a benign application. Unlike viruses, Trojan horses do not replicate themselves but they can be just as destructive. One of the most insidious types of Trojan horse is a program that claims to rid your computer of viruses but instead introduces viruses onto your computer.

TTL
Time To Live. A field in an IP header, indicating the length of time a packet is valid.

TTS
Text-To-Speech, a form of speech synthesis that converts text into spoken voice output. TTS systems were first developed to aid the visually impaired by offering a computer-generated spoken voice that would "read" text to the user. TTS should not be confused with voice response systems.

Tweening
Short for in-betweening, the process of generating intermediate frames between two images to give the appearance that the first image evolves smoothly into the second image. Tweening is a key process in all types of animation, including computer animation. Sophisticated animation software enables you to identify specific objects in an image and define how they should move and change during the tweening process.

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