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Theimportantthingto realizeisthatthere’smorethanonewaytoshowthe
samenumericvalue.Computerprogrammers,forexample,occasionallyuse
thehexadecimalsystembecauseit’s so compact.(Programmersoftenjust
say“hex”.)Thisbinarynumber:
101001011111110100110111111011010010110100001001
looksquiteabittidierwhenitiswrittenasA5FD37ED2D09,whichmeans
the samething.
The ASCII table
Wheredoes the Star LaserPrinter8 get the charactersand instructionsit
needsto print in the first place?It gets them from your computer,which
sendsa streamof textandcommandsto yourprinter.
Theprogramin yourcomputerthatcontrolseverythingsentto theprinter
(called the printer driver) will usually be includedwith your computer
programsrsuchasyourwordprocessor.Butthecommandscouldalsocome
fromaprogramyou’vewritten,perhapsinBASIC,aprogramminglanguage
thatusescommonEnglishwords.
Internally,computemand printersuse only the binarynumbersystemto
representboth commandsand all the alphabetic,numericand other key-
boardsymbols.Nearlyallof thosemachinesusethe sameschemeto code
thosesymbols,theAmericanStandardsCodefor InformationInterchange
(ASCII). ‘
Anexample:inourfamiliardecimalsystem,binary01001010addsuptothe
number 74. Dependingon which program your printer is using, it can
interpretthatbinarystring01001010aseitherthenumber74or thesymbol
J. Theprinterstoresthe symbolJ atposition74 in a tablein its memory.
Thateight-bitbinarystring,orbyte,canbebrokenintotwohalves.Theleft
or high-orderpartcontaining0100is calledthe zoneportion;therightpart
holdingthe 1010iscalledthedigitspdion. Andinthehexadecimalnumber
system,the zone and digit parts of that byte are representedas 4 and A
respectively(lookthemup in thelist above).
SothelaserprinterunderstandsthesymbolJ as 01001010,whichwecan
also representas the decimalnumber74 or the hexadecimalnumber4A.
We’veprintedthisbyteverticallyandhorizontallybelow,showinghowit
addsup to decimal74 andhex 4A.
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