eBook Dictionary Of Networking ShareReactor

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.Most computers run a simple set of systemdifferential backup A backup of a hardchecks when the computer is first turneddisk that includes only the information thaton.The PC tests are stored in ROM and arehas changed since the last complete backup.known as power-on self tests (POSTs).If aA differential backup assumes that a fullPOST detects an error condition, the com-backup already exists and that in the eventputer stops and displays an error messageof an accident, this complete backup willon the screen.be restored before the differential backupdialback modem See callback modem.is reloaded.106Copyright � 2000 SYBEX Inc., Alameda, CA.www.sybex.com2461book Page 107 Thursday, May 4, 2000 11:59 AMdigital signaldifferential SCSI A Small Computer Digital Equipment Corporation Ab-System Interface (SCSI) bus wiring scheme breviated DEC.A major manufacturer ofthat uses two wires for each signal on the minicomputers and mainframe computers,bus.One wire carries the signal, while the founded in 1957, long recognized for itsother carries its inverse.Differential SCSI high-quality computer systems.DEC sminimizes the effects of external interfer- most popular product line, the VAX series,ence and so allows longer SCSI cable ranges from small desktop systems to largelengths to be used.mainframes suitable for scientific and com-mercial processing.DEC was bought bySee also single-ended SCSI; Small Com-Compaq Computer Corporation in 1998.puter System Interface.For more information on DEC, seedigest A collection of Internet mailingwww.digital.com.list posts collected together and sent out asSee also DEC Alpha.a single large message rather than as a num-ber of smaller messages.Using a digest is aDigital Network Architecture Abbre-good way to cut down on the number ofviated DNA.The framework within whichnoncritical e-mail messages you receive.Digital Equipment Corporation (DEC) de-signs and develops all its communicationsSee also LISTSERV; listserver; mailing list.products.digital Describes any device that repre-digital service See digital signal.sents values in the form of binary digits orbits.digital signal Abbreviated DS; alsoknown as digital service.There are severalSee also analog.levels of common carrier digital transmis-sion service:digital audio tape Abbreviated DAT.Amethod of recording information in digitalDS-0 64Kbps.form on a small audio tape cassette, origi-DS-1 1.544Mbps (T1).nally developed by Sony and Hewlett-Pack-DS-1C Two DS-1 channels are multi-ard.The most common format is a 4-plexed into a single DS-1C 3.152Mbpsmillimeter, helical-scan drive, which canchannel.hold more than 3GB of information.DATscan be used as backup media; however, like DS-2 Two DS-1C channels are multi-all tape devices, they are relatively slow.plexed into one DS-2 6.312Mbps (T2)channel.Digital Data Communications Mes-DS-3 Seven DS-2 channels are multi-sage Protocol Abbreviated DDCMP.Aplexed into a single 44.736Mbps (T3)byte-oriented, link-layer synchronous pro-channel.tocol from Digital Equipment Corporation(DEC), used as the primary data-link com- DS-4 Six DS-3 channels are multiplexedponent of DECnet.into one 274.176Mbps (T4) DS-4 channel.107Copyright � 2000 SYBEX Inc., Alameda, CA.www.sybex.com2461book Page 108 Thursday, May 4, 2000 11:59 AMDigital Signal ProcessingThe higher-capacity channels are construct- DS-0 is also referred to as fractional T1,ed by multiplexing the lower-bandwidth because it bridges the gap between 56-Kbpschannels together, with some additional direct dial service (DDS) and a full T1framing and administrative overhead.implementation.DIGITAL SIGNALDigital Signal Processing Abbreviated digital signature An electronic signa-DSP.An integrated circuit used in high- ture that cannot be forged.A digital signa-speed data manipulation.You will find DSP ture confirms that the document or e-mailchips integrated into sound cards, modems, in question originated from the individualand video-conferencing hardware for use in or company whose name appears on thecommunications, image manipulation, and document and that the document has notother data-acquisition applications.been altered or tampered with in any waysince it was signed.See also codec; desktop video.See also certificate.108Copyright � 2000 SYBEX Inc., Alameda, CA.www.sybex.com2461book Page 109 Thursday, May 4, 2000 11:59 AMDIP switchDigital Subscriber Line Abbreviated per disc.DVD drives can also read conven-DSL.A high-speed data transmission tech- tional compact discs.nology originally developed by Bellcoredigital video disc-erasable Abbreviat-that delivers high bandwidth over existinged DVD-E.An extension to the digital videotwisted-pair copper telephone lines.disc format to allow multiple re-recordings.There are several DSL services, providingSee also digital video disc-recordable.data rates from 16Kbps to 52Mbps.Theservices can be symmetrical, with the samedigital video disc-recordable Abbrevi-data rate in both upstream and downstreamated DVD-R.An extension to the digital vid-directions, or asymmetrical, with the down-eo disc format to allow one-time recording.stream capacity greater than the upstreamSee also digital video disc-erasable.capacity.Asymmetric services are particu-larly suitable for Internet users, becausedigital video disc-ROM Abbreviatedmore information is downloaded than isDVD-ROM.A computer-readable form ofuploaded.digital video disc with either 4.7 or 8.5GBof storage per side.As DSL data rates increase, the distanceover which the service is provided decreas-dimmed command In a graphical useres; certain users who are located too farinterface, a command that is not currentlyfrom the telephone company s central of-available [ Pobierz całość w formacie PDF ]

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