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ZZ 1. symb. impedance. See impedance. 2. abbrev.Zulu time. See Zulu time. 3. abbrev. Zebra time. SeeZebra time. 4. symb. zetta-. See zetta. 5. The nameof a formal specification language for describing andmodeling computing systems, based on axiomatic settheory and predicate calculus. Z was developed atOxford University in the early 1980s.

Z axis A reference baseline or vector within a coor-dinate system, most often associated by conventionwith rectangular or Cartesian coordinates. The Z axisis oriented perpendicular to the X and Y axes in athree-dimensional system. See Cartesian coordi-nates, X axis, Y axis.

Z axis modulation The varying of the intensity ofan electron stream in a cathode-ray tube (CRT) bymanipulating the cathode or control grid.

Z code In telegraphy, a system of shortcut codes re-lated to short phrases to save transmissions time. Zcodes were those prefixed with Z, a rarely usedletter, to reduce the chance of confusing them withthe content of a message. For example, ZFB meantYour signal is FailingBadly.

Z force The pressure sensitivity of touch-activateddevices, such as touchscreen monitors or touch-sen-sitive pads, as are often used in kiosks.

Z Series Recommendations A series of ITU-T rec-ommendations providing guidelines for program-ming languages and general software aspects of tele-communications systems. These guidelines are avail-able as publications from the ITU-T for purchase onthe Net. Since ITU-T specifications and recommen-dations are widely followed by vendors in the tele-communications industry, those wanting to maxi-mize interoperability with other systems, or conformto software conventions widely used, need to beaware of the information disseminated by the ITU-T. A full list of general categories is listed in Appen-dix C and specific series topics are listed under indi-vidual entries in this dictionary, e.g., B Series Rec-ommendations. See Z Series Recommendationschart.

Z-80 The Zilog Z-80 8-bit computer microproces-sor was released in 1976 by the Zilog Corporationand was quickly incorporated into many control androbotics applications, and into a number of popularmicrocomputers such as the Tandy Radio Shack

Model I and LNW-80 computers. While it was ca-pable of clock rates up to 2.5 MHz, implementationsof 1.4 to 2.4 were common.

The Z-80 evolved from the Intel 8080 with which it

was more or less compatible; it was faster, with moreinstructions, not all of which were used to ensurecompatibility with 8080 systems. The Z-80 has asimple register structure, including index registersand an accumulator, and is capable of 16-bit address-ing through 8-bit double register pairs, something notfound on most of the other microprocessing chipsthat were incorporated into 8-bit microcomputers atthe time.

Many hobbyists acquired their first machine lan-guage and assembly language programming skillson the Z-80 chip. The original Z-80 was followedby faster versions, such as the Z-80A, Z-80B, andothers, and has been used for two decades in manycontrol applications such as robotics and telemetry,due to its simple efficiency, low cost, and practicalinstruction set. See TRS-80.

z-fold, zigzag fold, fanfold A term for a type of foldoften used in continuous-feed forms and other com-puter printouts. The name is derived from the shapeof three sheets of paper that alternately fold one wayor the other along the perforations. The design al-lows long lengths of paper to pass through a printerand refold on the other side to form a neat pile. Inthe printing industry, the z-fold is sometimes used

for company brochures and handouts, and typicallydoesnt require perforations unless a folded sectionis designed as a tear-off return sheet.

Z-marker See zone marker.

Z++ Just as C++ is seen as a more recent, object-oriented derivative of the C programming language,Z++ is an object-oriented extension of Z, a formalspecification language for describing computing sys-tems. See Z.

Z1 A historically important pioneer home-brewedbinary relay computer developed in Germany in themid-1930s by Konrad Zuse. While this was a sig-

nificant pioneering computer construction, it waslargely unknown outside of Germany due to the sec-ond World War and, as such, did not significantly in-fluence the industry abroad. It is noteworthy that itwas built in an apartment, rather than in a university

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research facility as were other pioneer computingplatforms. See Zuse, Konrad.

Z3 A historic programmable, general purpose com-puter, developed by Konrad Zuse. The Z3 was re-leased in 1941. See Z1, Zuse, Konrad.

zap slang To eradicate data, to burn out a circuit, orto apply charge to an object or environment. It mayor may not be intentional, and can result from powerfluctuations such as those caused by lightning (which

ITU-T Z Series Recommendations

Recom. Description

Z.100 Specification and descriptionlanguage (SDL)

Z.105 SDL combined with ASN.1 modules(SDL/ASN.1)

Z.106 Common interchange format for

SDLZ.107 SDL with embedded ASN.1

Z.109 SDL combined with UML

Z.110 Criteria for use of formal descriptiontechniques by ITU-T

Z.120 Message sequence chart (MSC)

Z.130 ITU object definition language

Z.140 The tree and tabular combinednotation version 3 (TTCN-3): Corelanguage

Z.141 The Tree and Tabular Combined

Notation version 3 (TTCN-3):Tabular presentation format

Z.200 CHILL - The ITU-T ProgrammingLanguage

Z.301 Introduction to the CCITT man-machine language

Z.302 The meta-language for describingMML syntax and dialogueprocedures

Z.311 Introduction to syntax and dialogueprocedures

Z.312 Basic format layout

Z.314 The character set and basic elements

Z.315 Input (command) language syntaxspecification

Z.316 Output language syntax specification

Z.317 Man-machine dialogue procedures

Z.321 Introduction to the extended MMLfor visual display terminals

Z.322 Capabilities of visual displayterminals

Z.323 Man-machine interaction

Z.331 Introduction to the specification ofthe man-machine interface

Z.332 Methodology for the specification ofthe man-machine interface - General

is probably where the term originated). You can zapa file to kill specific data (or the whole file), you canzap food in a microwave, and you can zap or fry acircuit by accidentally shorting it. The term is occa-sionally used to indicate a quick change, such as thechanging of a TV station with a remote, but this di-lutes the meaning of the term and is better avoided(unless perhaps its a lightning fast change) as zap isintended to describe an action or event that is poten-

tially dangerous, lethal, or destructive, especiallywhere electricity is involved. See kill.

zapper 1. A device or function that can apply a sud-den stimulus such as electricity or heat that affectsan immediate change such as a burn or incision. Ex-amples include shock devices such as a stun gun ora laser torch or scalpel. 2. A software utility thatcauses something to be instantly altered or removed,such as a file zapper that may be designed to seekout and permanently eradicate the entries of custom-ers who have not purchased anything for more thana year.

ZBTSI See zero byte time slot interchange.Zebra time, Z time The same as Greenwich MeanTime. See Greenwich Mean Time, Z.

Zeeman effect An effect observed in 1896 on thestructure of gas spectrum lines when subjected to theinfluence of a moderately strong magnetic field. Itwas observed by Pieter Zeeman that sharp spectrallines split into multiple closely spaced lines. Thisearly puzzle gave rise to a number of lines of researchin quantum physics. The number of lines is gener-ally three, although anomalous effects have beenobserved and even stronger magnetic fields can cause

some spectral lines to emerge.The Zeeman effect is a useful tool in a number ofareas of science including the study of laser light. Itis an intriguing effect to quantum physicists and isused by astrophysicists to map the magnetic fieldstrengths of solar effects and to study other galacticmagnetic fields.

The Zeeman effect is often described in associationwith the Stark effect that describes the influence ofstrong electrical fields on spectral lines. See Starkeffect.

Zen An Asian Buddhist system of belief that encour-ages meditation and self-discipline, and the attain-ment of enlightenment through direct intuitive ex-perience. Some aspects of Zen are unfamiliar toWesterners who are raised with different philoso-phies and customs, but it is nevertheless of interestto many and frequently referenced in philosophicalwritings about mathematics, physics, and telecom-munications.

Zen mail A tongue-in-cheek descriptive phrase forcomputer communications that erroneously (or de-liberately) arrive with no content in the body of themessage. See Zen.

zener current In an intense electric field, a currentthrough an insulator sufficient to excite an electronfrom the valence band to the conduction band.

zener diode An electronic component that behaveslike a rectifier below a certain voltage, but exhibits

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transmission reception, a system that uses locallygenerated voltage at the receiving end of the trans-mission, which is the same frequency as the origi-nal carrier and combines it with the incoming sig-nal. See beat reception, heterodyne.

zero bias 1. In a cathode-ray tube (CRT), the absenceof any difference in potential between the cathodeand its control grid. 2. In teletypewriter transmissioncircuits, zero bias is a state in which the length ofthe received signal matches the length of the trans-mitted signal.

zero bit insertion, bit stuffing In data communica-tions, the process of inserting a zero bit after a seriesof one bits in order to specify a distinct break orchange. Thus, the beginning or ending of a frame isnot misconstrued. This is sometimes used in placeof control signals.zero compression A data compression technique inwhich nonsignificant leading zeros are removed.

zero fill A data manipulation technique in which ze-ros are inserted into a file or transmission withoutaffecting the meaning of the data. See zero bit inser-tion.

zero insertion force ZIF. A type of socket used inintegrated circuits that allows a chip to be insertedwithout undue pressure. A lever or screw is thenpushed or turned to lock the component securely inplace so that it is not dislodged due to bumping ortransit. This type of socket costs more than standardpressure sockets and tends to be used in specializedsystems such as test systems or with specific chipsthat are larger or more expensive.

zero level A level established in order to have a ref-erence from which to judge further states or activi-ties of sounds and signals for observation, calibra-tion, or testing. The definition of zero level is tech-nology specific.

zero potential The potential of the Earth, used as areference measure.

zero power peripheral A device that requires verylittle power and consequently can draw that powerfrom the primary device to which it is attached, orfrom the circuit with which it is associated. Somemodems and most telephones take their power fromthe phone line, unless they have extra features (e.g.,

speakerphone) requiring additional power. Externalfloppy drives and pointing devices often draw powerfrom the laptops to which they are attached. Zeropower peripherals are favored in mobile communi-cations as they are less bulky than standard periph-erals with power supplies, and easier to attach, sinceextra electrical outlets are not required.

zero punch A punch located specifically in the thirdrow from the top of a punch card. See Hollerith card,punch card.

zero shift, zero drift A descriptive measure of theamount of shift or drift that has occurred from the

original setting or calibration point, at a subsequentpoint in time. See zero stability.

zero stability The ability of an instrument to retainits original state or settings over time, that is, towithstand zero shift. Zero stability is generally

a sudden increase in current-carrying capacity abovea specific voltage level (zener value) and a corre-sponding decrease in dynamic resistance resulting ina reverse breakdown. The dual nature (di-) makes itpossible to represent conducting and nonconducting(or very low conducting) states as a binary systemand the breakdown under reverse bias (functioningas an open circuit) is particularly useful as a refer-ence circuit or as a shutoff circuit to respond to

power surges above a certain voltage threshold.Doping is a manufacturing process in which elementssuch as rare earth elements are introduced into a sub-stance (e.g., fiber optic cable) to improve its quali-ties for a particular purpose such as the transmissionof laser light. Doping is also used in semiconductorsto influence their conducting qualities. Heavy dop-ing in pn junctions, for example, results in very thindepletion layers that hinder impact ionization butfacilitate quantum tunneling and the flow of current.This, in turn, leads to zener breakdown which issomewhat related to avalanche breakdown from im-

pact ionization, as may occur in lightly doped pnjunctions.

Zener diodes are used in voltage regulators andpower supplies and help prevent electrostatic dis-charge in a wide variety of semiconductor technolo-gies. They are becoming especially important in themobile communications industry because small por-table devices become vulnerable to voltage surges/static electricity when they are connected to otherdevices such as network cables, docks. Tiny zenerdiodes capable of absorbing static surges are thusbeing incorporated into mobile phones, pagers, etc.

zener effect A reverse-current breakdown effect thatoccurs at a semiconductor or insulator junction in thepresence of a high electric field. See zener current,zener diode.

Zenith Corporation One of the early entrants to theradio industry, Zenith was founded in 1931 by a ra-dio amateur and soon became a major manufacturer.Zenith now promotes consumer flat-screen, large-size television/media screens. Too bad the commer-cials arent as classy as the products.

zeppelin antenna A horizontally oriented antenna,which is a multiple of a half wavelength in length

with a two-wire transmission coming into one end,which is also a multiple of a half wavelength.

zepto- A standard metric prefix of the Systme In-ternationale (SI). The zepto unit is used in scientificmeasurement requiring very small numbers and rep-resents 1000-7 in decimal. See zetta-.

zero balancingA telephone service accounting tech-nique in which a specific dollar quantity is distrib-uted over a large category of calls. The total baseprice of all the calls within the category is used tocalculate an adjustment percentage so the full dollaramount produces a zero balance (rounding errors are

not permitted).zero beat In electronics and acoustics, a conditionduring which two combined frequencies match, andconsequently do not create a beat.

zero beat reception, homodyne reception In radio

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considered a desirable characteristic. See zero shift.zero stuffing See zero bit insertion.zero suppression The elimination of zeros that arenot meaningful. Zero suppression is often used toincrease the readability of information with leadingzeros, for formatting or transmission purposes, whichwould otherwise be distracting or confusing to a hu-man reader. In these cases, the zeros are often re-placed with a blank (a space character on printouts).Tables and columnar data (like financial statements)are usually printed with zero suppression.zero transmission level reference point For an ar-bitrarily selected point in a circuit, a level readingthat is subsequently used against which to measuretransmission levels in other points of the circuit orat the same point at another time. In telephone trans-missions, the reference point is frequently selectedat the location of the source of the transmission.zero usage customerA listed subscriber who has notused the network to which he or she has access.zerofill, zeroize To insert the zero character intounused storage locations. This is done for a varietyof reasons: for formatting, for creating space savers,and sometimes as a delay mechanism to match uptransmission speeds with output speeds of sloweroutput devices (printers, facsimile machines, etc.).zetta- Z. A standard metric prefix of the Systme In-ternationale (SI). The zetta unit is used in scientificmeasurement requiring very large numbers and rep-resents 1021 or 1,000,000,000,000,000,000,000 or10007 in decimal. See yotta-, zepto-.ZIF See zero insertion force.Zimmermann, Philip R. A software engineer andcryptography specialist, best known for developingthe Pretty Good Privacy (PGP) encryption schemebased upon the Blowfish technology, Zimmermannis the founder of PGP, Inc. He is a software engineerwith a long history of experience in cryptography,data security, data communications, and realtime em-bedded systems development.Zimmermann has been honored with numerous hu-manitarian awards due to his contribution to the safe-guarding of personal privacy, including the 1996Norbert Wiener Award, the 1995 Pioneer Award fromthe Electronic Frontier Foundation, and many more.

Zimmermann is a member of the International As-sociation of Cryptologic Research, the Associationfor Computing Machinery (ACM), and others. SeeBlowfish, PGP Inc., Pretty Good Privacy.zinc Zn. A malleable, bluish metallic element with arelatively high electropotential, useful in plating, dip-ping, and galvanizing, to prevent corrosion in othermetals. Combined with copper, it forms brass, usedfor piping, construction accessories, and householditems.zip v. To bundle up or compress a file or set of files,usually for transferring or archiving. The term is now

commonly used for any such processing (zipping)of files, regardless of the archive utility used, butoriginally referred to programs called gzip andPKZIP. See arc, compress, gzip, PKZIP, uuencode.ZIP Zone Information Protocol.

zip code A series of characters added to a mail ad-dress that specifies the destination in order to expe-dite delivery. In Canada and the U.K. (calledpostalcode), it consists of numbers and letters. In the U.S.it consists of five digits, a hyphen, and four additionaldigits more recently introduced as a routing code. Zipcodes can be optically scanned and converted intobar codes for processing by automated mail systems.

zipped See zip, gzip, PKZIP.

Ziv See Lempel-Ziv.

ZModem A fast, flexible, error-correcting, full-du-plex file transfer data transmission protocol similarto XModem and YModem, but with updates and en-hancements. YModem and ZModem were written byChuck Forsberg.

ZModem is well supported by various telecommu-nications programs, and many BBSs and servicebureaus use it.

ZModem includes fallback and dynamic adjustmentof packet size, which is important if the connection

is a line with fluctuating characteristics. One ofZModems most valuable features is its ability to re-sume a file transfer that has been aborted. With al-most all earlier desktop serial file transfer programs,if the line was interrupted or the file transfer aborted99% of the way through, the program would startagain from the beginning when reconnected, ratherthan resuming from where it left off. ZModem candetect a partial file, establish a new starting point atthe end of the partial file, and continue transmittinguntil the transfer is completed or interrupted. Ifyouve ever spent a couple of hours transferring avery large file on a slow link and lost it when thetransmission was almost complete, you will appre-ciate ZModems resume feature. See XModem,YModem.

ZOG A high-performance frame- and link-basedhypertext system designed for local area networks(LANs) developed at Carnegie Mellon University.It has evolved into a commercial product calledKnowledge Management System (KMS).

zone 1. An area, usually contiguous, which may ormay not be self-contained; or has some commoncharacteristics within itself; or which is distinguishedas different, in some way, from the surrounding area;or which is assigned on the basis of size, population,or some other economic or practical characteristic(as in shipping zones). 2. A section of computer stor-age allocated for a particular purpose. 3. In telephonecommunications, a specified area outside the localexchange. 4. In cellular phone communications, azone consisting of adjacent cells is called a cluster.5. A region in which communications are banned orimpeded, called a blackout zone. 6. A physical or vir-tual region of access within a network, sometimesdelineated by physical structures such as a worksta-tion or router. See firewall.

zone, optical recognition A region manually speci-fied by the user, or automatically detected and en-closed by the optical recognition software, that cor-responds to a particular type of information. Forexample, some optical document recognition

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systems, and some of the better optical character rec-ognition systems, can distinguish columns and pagenumbers, images and formulas, and scan each sepa-rately from the others. Some software allows zonesto be set up in a template in advance and order pri-ority to be assigned to the zones. In this way a longdocument, such as a book in which most of the pagesare identical in format, can be scanned without re-setting the zones each time.

Many optical recognition programs will automati-cally determine zones or allow them to be manuallyconfigured. This allows the flow of text, and separa-tion of graphics and text to be handled more efficientlyby the software, as in this Caere Omnipage example.

zone, punch card One of three specific positions onthe top of a punch card. See punch card, zone punch.

zone blanking Turning off a cathode-ray tube (CRT)at a point in the sweep of an antenna.zone cabling A cabling architecture designed foropen office systems in which various physical zonesare designated and cabled so that office desks andequipment can be moved around without ever beingtoo far from the various necessary outlets and con-nectors.

zone marker, Z-marker A vertically radiating bea-con of light that signals a zone above a radio stationtransceiver.

zone method A wire installation ceiling distribution

system in which the space above rooms is organizedinto sections or zones. Cables are centralized in eachzone, with main arteries running between zones orto the central power source. See distribution frame.

zone of authority The set of names managed by, or

under the authority of, a specific name server.

zone of silence, skip zone In radio transmissions, ageographic region that does not receive normal ra-dio signals, frequently due to abrupt changes in ter-rain, (e.g., mountains).

zone paging The capability of an intercom or phonesystem to selectively page certain groups of speak-ers. See public address system.

zone punch In a punch card, a punch located in oneof the upper three rows (the section that usually hasless text displayed on the card). See Hollerith card,punch card. Contrast with digit punch.

zone time A system in which the Earth is dividedlongitudinally into 24 time zones of about 15 degreeseach starting in Greenwich, England. It was devel-oped in the late 1800s by a Canadian, S. Fleming, toestablish a standard time. See Greenwich MeanTime.

zoning, stepping In microwave transmissions, dis-placement of portions of the surface of the micro-

wave reflector in order to prevent changes in thephase front in the near field.

zoom To continuously reduce or enlarge an image,as on a monitor or in a viewfinder. Zooming capa-bility is usually provided to improve the visibility ofdetails (zoom in), or to provide a big picture, wideangle view (zoom out) of a diagram, object, image,or scene. See zoom factor.

zoom factor The degree to which an image can bescaled, that is, decreased or enlarged. The X and Yaxes may or may not be capable of sizing indepen-dent of one another. The enlargement zoom factoron consumer camcorders often ranges from 20 to 200times (or more) the normal viewing factor. In somecases, the zoom factor on still cameras and cam-corders may be digitally enhanced, that is, the zoomup to 20 times may be an optical zoom and, beyondthat, it may be a digital zoom, which may show somepixelation at higher zoom factors. See zoom.

zoom lens An apparatus that provides the ability toreduce or enlarge the apparent size of an image inorder to frame that image with the desired scope orto enhance detail. Commonly used on video and filmcameras, and sometimes on telescopes and binocu-lars.

zsh, Z shell A Unix command interpreter shell, simi-lar to ksh, developed by Paul Falstad. Zsh is said tobe similar to a bash shell, but faster and with morefeatures. Zsh is not a Posix-compliant implementa-tion.

Zulu time Greenwich Mean Time, CoordinatedUniversal Time.

Zuse, Konrad (1910-1995) A German structuralengineer and inventor who independently createdpioneer general purpose calculating and computingtechnologies, coincident with the development of theAttanasoff-Berry computer in the U.S. and AlanTurings computing theories in England. Zuses ac-complishment is remarkable, considering he didnthave the corporate and university facilities, funding,and personnel support that led to the developmentof other pioneer computing systems.

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Zuse began building computers in his mid-20sfrom a studio he set up in his parents apartment.He reports in his autobiography that he originatedthe concept in 1934, and constructed the V1, latercalled the Z1, between 1936 and 1938. His earlynotebooks describe important binary computing con-cepts. The Z1 included mechanical memory for datastorage (for practical reasons of space and ease ofconstruction) and used program instructions punchedinto film. Later, Zuse added the Z2, Z3 and Z4, witha friend, Helmut Schreyer, providing expertise onelectronic relays and vacuum tubes. Zuse consideredhis Z3 relay-based version to be a true binary com-puter (the original Z3 was destroyed after World WarII bombing raids). A reproduction has been installedin the Deutsches Museum. The Z4, which began de-velopment in 1942, was demonstrated in April 1945,and operated in Zrich from 1950 to 1955. FromZuses agile mind came also a pioneer algorithmic

programming language called PlanKalkel (plancalculus) that was developed in the mid-1940s. SeeAttanasoff-Berry computer; Hertzstark, Curt.Zworykin, Vladimir Kosma (1889-1982) A Rus-sian-born American physicist and electrical engineerwho emigrated to America in 1919 and worked forWestinghouse Electric Company in the 1920s.Zworykin developed an idea to control the passageof beams in an electron tube with magnets to devisea cathode-ray tube (CRT), which he patented in 1928.This historic CRT led to his development of theiconoscope, a practical television camera. In 1929Zworykin demonstrated a cathode-ray-based displaydevice, the same basic concept as current computerand television monitors. In the same year, Zworykinbecame the director of research for the Radio Cor-poration of America (RCA). In November 1935, hereceived a patent for his apparatus for producing im-ages (U.S. #2,021,907).

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