Theimportantthingtorealizeis thatthere’smorethanone waytoshow the
samenumericvalue.Computerprogrammers,forexample,occasionallyuse
thehexadecimalsystembecauseit’s socompact.(Programmersoftenjust
say“hex”.)This binarynumber:
10100101111111010011011111101101OO1O11O1OOOO1OO1
looksquiteabittidierwhenitiswrittenas A5FD37ED2D09, whichmeans
thesame thing.
1.2.2The ASCIItable
Wheredoes the StarLaserPrinter4get the charactersand instructionsit
needsto print in thefirst place’?Itgets themfmm your computer,which
sendsastreamof text andcommandsto yourprinter.
Theprogram inyour computerthatcontrolseverythingsentto the printer
(calledthe printer driver) will usually be includedwith your computer
programs;suchasyourwordprocessor.Butthecommandscouldalsocome
fromaprogramyou’vewritten,perhapsinBASIC,aprogramminglanguage
thatuses commonEnglishwords.
Internally,computemandprinters useonly the binary numbersystemto
representboth commandsand all the alphabetic,numericand other key-
boardsymbols.Nearlyall ofthose machinesusethe sameschemeto code
thosesymbols,the AmericanStandardsCodeforInformationInterchange
(ASCII).
Anexample:inourfamiliardecimalsystem,binary01001010addsuptothe
number74. Depending on whichprogram your printer is using, it can
interpretthatbinarystring01001010aseitherthenumber 74orthe symbol
J. Theprinter storesthesymbolJat position74in atable inits memory.
Thateight-bitbinarystring,orbyte, canbebrokenintotwo halves.Theleft
orhigh-orderpartcontaining0100is calledthe zoneportion;theright part
holdingthe1010iscalledthedigitsportion.Andinthehexadecimalnumber
system,the zone and digit partsof that byte are representedas 4and A
respectively(lookthemup in the listabove).
Sothe laserprinterunderstandsthesymbolJas 01001010, whichwe can
alsorepresent asthe decimalnumber 74or the hexadecimalnumber4A.
We’veprintedthisbyte verticallyandhorizontallybelow,showinghowit
addsup to decimal74 andhex 4A.
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