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1.2.3HowyourIaserprinter communicates
Yourcomputercommunicateswiththe StarLaserPrinter4 througheither
apardef cableoroneoftwokindsof serialcable.Theprinter’sinterjzce,
the link or boundaryit shares with your computer,defineswhetherthe
printerwillacceptcharactersandcommandsfromyourcomputeronebyte
or one bit at a time.
Abitisthesmallestunitofcomputerorprintermemory.Ithaseitheralow
orhighelectriccharge,whichwerepresentwiththedigitsOand 1.Usually
eight adjacentbits are grouped to form a byte. Since a byte normally
representsonecharacter,thisstringofbits- O1OOOOO1—mightrepresent
the letterA.
The serialinterfaceacceptsjust one bit at a timefrom your computer.A
parallelinterfacecanhandleawholebyteatonce,bymovingdatabitsside-
by-sidealongseparatewires.Youchoosewhichinterfacemethodyouwant
to useby selectingit onthecontrolpanel,as explainedin yourStarLuser-
Printer4 OperationsManual.
1.2.4 TheStar LaserPrinter4 is a computer
TheStarLaserPrinter4 firstmapsthecharactemto beprintedintoitsown
randomaccessmemory(RAM).Thatis,theprinterbuildsa “picture”in its
memorycorrespondingtothepageyouwanttoprint.Whenthat’sdonethe
printercanreproducethepageontopaperonitsown,lettingyourcomputer
geton withotherwork.
YourStarLaserPrinter4 comeswithonemegabyteofRAM—theequiva-
lentof aboutonemillioncharacters.A StarLaserPrinter4 optionlets you
addasecondmegabyteofRAMif,say,youneedtomapfull-pagegraphics
or stemmorefonts. AccompanyingallthatRAMis another512kilobytes
of readonlymemory(ROM),containingalibraryof internalfontsandthe
programsthatlet the StarLaserPrinter4 emulateotherprinters.
An Intel 80960KAcomputer chip controls both the memory and the
printingmechanisminthepnnter,calledtheprintengine.Theprinterstores
a whole page in RAM before printingit. (If a page is so dense that it
overflowsmemory-a mostunlikelyevent—theStarLaserPrinter4 prints
thepage ontwo sheets.)
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