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Unformatted text preview: coding for the word STAR in ASCII-8 will be
B3/S B4/T A1/A B2/R = STAR
Since each character in ASCII-8 requires one byte for its representation and there are 4
characters in the word STAR, 4 bytes will be required for this representation.
The value of an alphanumeric or alphabetic data element is usually the name of some
object. Obviously one would not like to perform any arithmetic on such data but one may
like to compare them in order to arrange them in some desired sequence. Now, if we
compare the alphabetic values A and B, which one will be treated as greater by the
computer? For an answer to such questions, it is necessary to have some assigned
ordering among the characters used by the computer. This ordering is known as the
Collating sequence may vary from one computer system to another depending on the type
of computer code used by a particular computer. To illustrate this, let us consider the
computer codes already discussed in this chapter. Observe from Figures 4.2 and 4.3 that
the zone values of the characters A through 9 decrease in BCD code from the equivalent
of decimal 3 down to 0, while the zone values of the characters A through 9 increases in
EBCDIC from the equivalent of decimal 12 to 15. This means that a computer, which
uses BCD code for its internal representation of characters will treat alphabetic characters
(A, B, ..., Z) to be greater than numeric characters (0, 1, ..., 9). On the other hand, a
computer, which uses EBCDIC for its internal representation of characters will treat numeric characters to be greater than alphabetic characters. Similarly, observe from
Figure 4.6 and 4.7 that a computer, which uses ASCII for its internal representation of
characters will place numbers ahead of letters during a sort (ascending) because the
number characters have a zone value that is less than the zone value for letters.
However, whatever may be the type of computer code used, in most (not all - in BCD 0 >
9) collating sequences, the following r...
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This document was uploaded on 04/07/2014.
- Spring '14