Representing text

Counting symbols we can represent most "plain" textual documents as a sequence of symbols (i.e., ignoring mark-up such as boldface, page layout, etc.) The symbols themselves can be represented as sequences of bits: 7 or 8 bits per symbol is the norm, thus between 128 and 256 possible symbols (also called "characters")

Representing text

	Counting symbols
	The ASCII code The American Standard Code for Information Interchange (or ASCII) uses 7 bits per symbol to represent English letters, Arabic numerals, punctuation and a few control characters (e.g., "end-of-file", "carriage return", "bell", etc.). Several other codes were used historically (e.g., EBCDIC on IBM computers), but are used only rarely today. Here's a link to some info on ASCII

Representing text

	Counting symbols
	The ASCII code
	8-bit codes: the use of parity 8 bits are more natural than 7 in most computer applications (since 8 is a power of two); the "extra bit" is sometimes used as a safeguard against data corruption introduced by transmission errors and other "noise" For example, we can set the eighth bit to 0 if the number of 1 bits in the code is even or 1 if it is odd; this allows us to detect transmission problems where any single bit is corrupted

Representing text

	Counting symbols
	The ASCII code
	8-bit codes: the use of parity
	8-bit codes: modern symbol sets in many modern computer systems (Macintosh, Windows), eight bits are used to extend the symbol set to include, e.g., accented letters, the British pound symbol, etc.. This approach may cause problems when transmitting between newer and older systems and also conflicts with its use for parity checking.

Representing text

	Counting symbols
	The ASCII code
	8-bit codes: the use of parity
	8-bit codes: modern symbol sets
	Unicode: a new 16-bit standard a recent international standard called Unicode allows for 16 bits per symbol, thus greatly extending the range of symbols that can be acommodated (more than 65,000), including those used by almost every written language on Earth Here's a link to the Unicode home page and another one to a techincal introduction

Representing text

	Counting symbols
	The ASCII code
	8-bit codes: the use of parity
	8-bit codes: modern symbol sets
	Unicode: a new 16-bit standard
	Problems with Unicode unfortunately, not every language could be completely acommodated in the Unicaode, so that some older symbols used in Chinese, for example, had to be left out. This led to legitimate and serious concerns about fair representation for some cultures New modifications to the Unicode standard have tried to address these concerns by adding capacity for over a million characters if necessary. Newly proposed scripts include Tengwar, Klingon and many others