Character Sets, Code Pages, and Character Maps
In computer science, the terms character encoding, character map, character set or code page were historically synonymous, as the same standard would specify a repertoire of characters and how they were to be encoded into a stream of code units – usually with a single character per code unit. The terms now have related but distinct meanings, reflecting the efforts of standards bodies to use precise terminology when writing about and unifying many different encoding systems. Regardless, the terms are still used interchangeably, with character set being nearly ubiquitous.
A code page usually means a byte oriented encoding, but with regard to some suite of encodings (covering different scripts), where many characters share the same codes in most or all those code pages. Well known code page suites are "Windows" (based on Windows-1252) and "IBM"/"DOS" (based on code page 437), see Windows code page for details. Most, but not all, encodings referred to as code pages are single-byte encodings (but see octet on byte size.)
IBM's Character Data Representation Architecture (CDRA) designates with coded character set identifiers (CCSIDs) and each of which is variously called a charset, character set, code page, or CHARMAP.
The term code page does not occur in Unix or Linux where charmap is preferred, usually in the larger context of locales.
Contrasted to CCS above, a character encoding is a map from abstract characters to code words. A character set in HTTP (and MIME) parlance is the same as a character encoding (but not the same as CCS).
Legacy encoding is a term sometimes used to characterize old character encodings, but with an ambiguity of sense. Most of its use is in the context of Unicodification, where it refers to encodings that fail to cover all Unicode code points, or, more generally, using a somewhat different character repertoire: several code points representing one Unicode character, or versa (see e.g. code page 437). Some sources refer to an encoding as legacy only because it preceded Unicode. All Windows code pages are usually referred to as legacy, both because they antedate Unicode and because they are unable to represent all 221 possible Unicode code points.
Read more about this topic: Character Encoding
Famous quotes containing the words character, code and/or maps:
“A character is like an acrostic or Alexandrian stanza;—read it forward, backward, or across, it still spells the same thing.”
—Ralph Waldo Emerson (1803–1882)
“Hollywood keeps before its child audiences a string of glorified young heroes, everyone of whom is an unhesitating and violent Anarchist. His one answer to everything that annoys him or disparages his country or his parents or his young lady or his personal code of manly conduct is to give the offender a “sock” in the jaw.... My observation leads me to believe that it is not the virtuous people who are good at socking jaws.”
—George Bernard Shaw (1856–1950)
“And at least you know
That maps are of time, not place, so far as the army
Happens to be concerned—the reason being,
Is one which need not delay us.”
—Henry Reed (1914–1986)