Information Technology Reference
In-Depth Information
was to represent each as a sequence of zeros and ones, as bits, so
that the computer could interpret them. Several variations were
developed, but 7bit or 8bit codes were commonly used, so each
character was stored as 1 byte of data. After all, 1 byte can hold
256 different bit sequences, and this number is adequate for list
ing all uppercase letters, lowercase letters, digits, and basic
punctuation.
Details of coding are not particularly important as long as a
coding system contains an agreement about which sequence of bits
represents which character. Two common encodings for the Roman
alphabet soon emerged. Large computers typically used the
Extended
Binary Coded Decimal Interchange Code
(
EBCDIC
), particularly
when punch cards were common for data storage, whereas small
machines often used the
American Standard Code for Information
Interchange
(
ASCII
). See the sidebars on EBCDIC and ASCII for
some historical background on the development of each of these
coding systems.
ASCII
ASCII is a 7bit code that was developed as part of an effort to facilitate the sending
and receiving of information electronically. Much of the early work on ASCII came
from a group at IBM, headed by Robert W. Bemer. An early paper describing the work
was published in 1960. Bemer and his group worked to create both a draft coding
system and equipment to communicate with it. In May 1961, this work led to a pro
posal to the American National Standards Institute (ANSI). ANSI, in turn, proposed a
national standard in 1963, and a final ANSI Standard X3.4 for ASCII was established
in 1968. During this process, considerable work was done to ensure that the ASCII
ANSI Standard would be compatible with the international standards. Early computers
often used teletypes, a form of electrified typewriters, for input and output, so care
also was taken that the ASCII coding system would be compatible with the idiosyn
crasies of teletypes.
Over the years, several national variants of ASCII have emerged to meet the needs of
various languages. The International Organization for Standardization (ISO) now de
fines a family of 8bit coding standards based on ASCII for various alphabets. In such
8bit codes, the original 7bit coding usually is extended by adding a 0 bit at the
front, and newly added characters have an 8bit code that begins with a 1. For exam
ple, ISO Latin 1 uses the traditional ASCII for its first 128 characters, and then fills
out the remaining 128 characters with letters containing various accents and other
letters needed for Western European alphabets.
