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The important thing to realize is that there’s more than one way to show the
same numeric value.Computerprogrammers, forexample, occasionally use
the hexadecimal system because it’s so compact. (Programmers often just
say “hex”.) This binary number:
101001011111110100110111111011010010110100001001
looksquiteabittidier when itis written as A5 FD 37 ED 2D09, which means
the same thing.
1.2.2 The ASCII table
Where does the Star LaserPrinter 4111get the characters and instructions it
needs toprintinthefirstplace?Itgets themfrom yourcomputer, which sends
a stream 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
from a program you’ve written, perhaps inBASZC,aprogramming language
that uses common English words.
Internally, computers and printers use only the binary number system to
representbothcommands and allthealphabetic,numeric and other keyboard
symbols. Nearly all of those machines use the same scheme to code those
symbols,theAmerican StandardsCodeforInformationInterchange(ASCII).
An example: in our familiar decimal system, binary 01001010 adds up to the
number 74. Depending on which program your printer is using, it can
interpret that binary string 01001010 as either the number 74 or the symbol
J. The printer stores the symbol./ at position 74 in a table in its memory.
That eight-bit binary string, or byte.,can be broken into two halves. The left
or high-order part containing 0100 is called the zone portion; the right part
holding the 1010iscalled thedigitsportion.And in the hexadecimal number
system, the zone and digit parts of that byte are represented as 4 and A
respectively (look them up in the list above).
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