ASCII
The American
Standard Code for Information Interchange is a standard seven-bit code that
was proposed by ANSI (American National Standards Institute)
in
1963, and finalized in 1968. Other sources also credit much of the work on
ASCII to work done in 1965 by Robert W. Bemer.
ASCII was established to achieve compatibility between various types of
data processing equipment.
ASCII, pronounced "ask-key", is the
common code for microcomputer equipment. The standard ASCII character set
consists of 128 decimal numbers ranging from zero through 127 assigned to
letters, numbers, punctuation marks, and the most common special characters
(see ASCII Table).
ASCII Table
Computers
can only understand numbers, so an ASCII code is the numerical representation
of a character such as 'a' or '@' or an action of some sort. ASCII was
developed a long time ago and now the non-printing characters are rarely used
for their original purpose. ASCII was
actually designed for use with teletypes and so the descriptions are somewhat
obscure. If someone says they want your CV however in ASCII format, all this
means is they want 'plain' text with no formatting such as tabs, bold or
underscoring - the raw format that any computer can understand. This is usually
so they can easily import the file into their own applications without
issues. For instance, Notepad creates
ASCII text, or in MS Word you can save a file as 'text only'.
As people gradually required computers to understand
additional characters and non-printing characters the ASCII set became
restrictive. As with most technology, it took a while to get a single standard
for these extra characters and hence there are few varying 'extended' sets. The Extended ASCII Character Set also consists of 128 decimal numbers and
ranges from 128 through 255 representing additional special, mathematical,
graphic, and foreign characters (see Extended ASCII Table).
Extented ASCII Table
ASCII is not the only format in use out there. IBM adopted EBCDIC
(Extended Binary Coded Decimal Interchange Code) developed for punched cards in
the early 1960s and still uses it on mainframes today. It is probably the next
most well known character set due to the proliferation of IBM mainframes (see
EBCDIC Table).
A set
of national character sets for interchange of documents between IBM mainframes.
Most EBCDIC character sets do not contain all of the characters defined in the
ASCII code set but there is a special International Reference Version (IRV)
code set that contains all of the characters in ASCII. Several national
versions have been updated to support the encoding of the euro sign (in lieu of
the currency sign).
Unlike virtually every computer system in the
world which uses a variant of ASCII, IBM mainframes and midrange systems such
as the AS/400 tend to use a wholly incompatible character set primarily
designed for ease of use on punched cards.
EBCDIC uses the full 8 bits available to it, so parity checking cannot
be used on an 8 bit system. Also, EBCDIC has a wider range of control
characters than ASCII.
EBCDIC Table
