The importantthing to realize is that there’s more than one way to show the
samenumeric value. Computerprogrammers, for example,occasionally use
the hexadecimal system because it’s so compact. (Programmers oftenjust
say “hex”.) This binary number:
101001011111110100110111111011010010110100001001
looksquite abittidier whenit iswritten as A5FD 37 ED2D 09,which means
the same thing.
1.2.2 TheASCII table
Where does the Star LaserPrinter 4111get the characters and instructions it
needsto printin thefirstplace? Itgets themfrom your computer,which sends
astream of text and commands to your printer.
The program in your computer that controls everything sent to the printer
(called the printer driver) will usually be included with your computer
programs,such as your word processor. But the commands could also come
fromaprogram you’ve written, perhaps in BASZC,aprogramming language
that usescommon English words.
Internally, computers and printers use only the binary number system to
representboth commandsand allthe alphabetic,numeric andother keyboard
symbols. Nearly all of those machines use the same scheme to code those
symbols,theAmerican Standards CodeforInformation Interchange(ASCII).
Anexample: in our familiardecimal system, binary01001010 adds up to the
number 74. Depending on which program your printer is using, it can
interpretthat binary string 01001010 as either the number 74 or the symbol
J. The printer storesthe symbol./ at position 74 in atable in its memory.
Thateight-bit binary string, or byte.,can be broken into two halves. The left
orhigh-order part containing 0100 is called the zone portion; the right part
holdingthe 1010 iscalledthe digitsportion. And inthe hexadecimalnumber
system, the zone and digit parts of that byte are represented as 4and A
respectively (look them up in the listabove).
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