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The importantthingto realizeis thatthere'smorethanone wayto showthe
samenumericvalue.Computerprogrammers, f orexample,occasionally use
the hexadecimalsystembecauseit's so compact.(Programmersoftenjust
say "hex".)This binarynumber:
1010010111111101001101 11111011010010110100001001
looksquiteabittidierwhenitis writtenasA5FD37ED2D09,whichmeans
the same thing.
The ASCII table
Where does the Star LaserPrinter8 get the charactersand instructionsit
needs to print in the first place? It gets them from your computer,which
sendsa streamof text and commandsto yourprinter.
The programin your computerthat controlseverythingsent to the printer
(called the printer driver) will usually be included with your computer
programsrsuchas yourwordprocessor.Butthecommandscouldalsocome
froma programyou'vewritten,perhapsinBASIC,aprogramminglanguage
that uses commonEnglishwords.
Internally,computemand printersuse only the binary number system to
representboth commandsand all the alphabetic,numeric and other key-
board symbols.Nearlyall of thosemachinesuse the same schemeto code
those symbols,the AmericanStandardsCodefor InformationInterchange
(ASCII).
'
Anexample:in ourfamiliardecimalsystem,binary01001010addsup tothe
number 74. Dependingon which program your printer is using, it can
interpretthatbinarystring01001010as eitherthenumber74 or the symbol
J. The printer storesthe symbolJ at position74 in a table in its memory.
Thateight-bitbinarystring,or byte,can bebrokenintotwohalves.The left
or high-orderpart containing0100is calledthe zoneportion;the rightpart
holdingthe 1010iscalledthedigitspdion. Andinthehexadecimal n umber
system,the zone and digit parts of that byte are representedas 4 and A
respectively(lookthem up in the list above).
So the laser printerunderstandsthe symbolJ as 01001010, which we can
also representas the decimalnumber74 or the hexadecimalnumber4A.
We'veprintedthis byteverticallyand horizontallybelow,showinghow it
addsup to decimal74 and hex 4A.
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