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The important thing to realize is that there’s more than one way to show the
same numeric value. Computer programmers, for example, occasionally use
the hexadecimal system because it’s so compact. (Programmers often just
say “hex”.) This binary number:
101001011111110100110111111011010010110100001001
looks quite a bit tidier when it is written as A5 FD 37 ED 2D 09, which means
the same thing.
The ASCII table
Where does the Star LaserPrinter 8111 get the characters and instructions it
needs to print in the first place? It gets them from your computer, 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 in BASIC, a programming language
that uses common English words.
Internally, computers and printers use only the binary number system to
represent both commands and all the alphabetic, numeric and other key-
board symbols. Nearly all of those machines use the same scheme to code
those symbols, the American Standards Code for Information Interchange
(ASCII).
Anexample: inourfamiliardecimal system, binary01001010 adds up to the
number 74. Depending on which program your printer is using, it can
interpret that binary string 010010 10 as either the number 74 or the symbol
J . The printer stores the symbol J 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 1010 is called the digits portion. 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).
So the laser printer understands the symbol J as 01001010, which we can
also represent as the decimal number 74 or the hexadecimal number 4A.
We’ve printed this byte vertically and horizontally below, showing how it
adds up to decimal 74 and hex 4A.
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