Information Technology Reference
In-Depth Information
dex was recomputed and corrected over the weekend of November 26, 1983.
Specifically, when trading concluded on November 25, the Vancouver Stock
Exchange Index was quoted as 524.811; the corrected figure used to open on
Monday morning was 1098.892. The correction for 22 months of compounded
error caused the Index to increase by 574.081 over a weekend without any
changes in stock prices. In this example, computations began with correct
data, but subsequent processing introduced a significant error in the result.**
** From
The Limits of Computing
, pp. 100-101.
As this example suggests, the storage and processing of floating
point numbers often are subject to numerical error. As a practical
matter, this means that we may need to be careful in interpreting re
sults from computers. For example, some analysis of accuracy may
be appropriate before giving great significance to computergener
ated answers, especially if decisions must be based on many digits
of accuracy.
How does a computer know to use a Roman
Russian, Greek, or other languages?
In the early days of electronic computing (perhaps the 1900s
through 1970 or even 1980), much of the experimentation with and
development of technology occurred in America and Great Britain.
In these environments, researchers typically used English as their
primary (or only) language, and therefore developed textbased sys
tems for computers with a 26letter Roman alphabet in mind. Other
computer development occurred in Europe, but most of these peo
ple also used a Roman alphabet. Further, because most hardware
came from U.S. manufacturers, researchers in nonEuropean coun
tries often began with equipment based on the Roman alphabet and
basic English punctuation.
With the domination of English for communication, the
challenge for early computer manufacturers was to find a
reasonable way to represent English letters, digits, and punctua
tion so that they could be interpreted electronically. Although
these characters certainly are not numbers, the basic approach
