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Theimportantthingto realizeisthatthere’smorethanonewayto showthe
samenumericvalue.Computerprogrammers,forexample,occasionallyuse
thehexadecimalsystembecauseit’s so compact.(Programmersoftenjust
say“hex”.)This binarynumber:
10100101111111010011011111101101OO1O11O1OOOO1OO1
looksquiteabittidierwhenitiswrittenasA5FD37ED2D09,whichmeans
the samething.
1.2.2 TheASCII table
Where doesthe Star LaserPrinter4 get the charactersand instructionsit
needsto print in the firstplace’?It getsthem fmm yourcomputer,which
sendsa streamof textandcommandsto yourprinter.
The programin yourcomputerthatcontrolseverythingsentto theprinter
(called the printer driver) will usually be includedwith your computer
programs;suchasyourwordprocessor.Butthecommandscouldalsocome
fromaprogramyou’vewritten,perhapsinBASIC,aprogramminglanguage
thatuses commonEnglishwords.
Internally,computemand printersuse only the binarynumbersystemto
representboth commandsand all the alphabetic,numericand other key-
boardsymbols.Nearlyallof thosemachinesuse the sameschemeto code
thosesymbols,the AmericanStandardsCodefor InformationInterchange
(ASCII).
Anexample:inourfamiliardecimalsystem,binary01001010addsuptothe
number 74. Dependingon which program your printer is using, it can
interpretthatbinarystring01001010aseitherthenumber74orthesymbol
J. The printerstoresthe symbolJ atposition74in a tablein itsmemory.
Thateight-bitbinarystring,or byte,canbebrokenintotwohalves.Theleft
or high-orderpartcontaining0100is calledthezoneportion;the rightpart
holdingthe 1010iscalledthedigitsportion.Andinthehexadecimalnumber
system,the zone and digit parts of that byte are representedas 4 and A
respectively(lookthemup in the listabove).
So thelaserprinterunderstandsthesymbolJ as 01001010,whichwe can
also representas the decimalnumber74 or the hexadecimalnumber4A.
We’veprintedthisbyteverticallyandhorizontallybelow,showinghowit
addsup to decimal74 andhex4A.
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