ASCII is a character set used to display characters on a computer screen. It uses seven bits to define each letter and includes control characters. The Unicode character set is a contender for replacing ASCII and allows for unlimited characters. ASCII art uses the basic character set to create visual images.
ASCII stands for American Standard Code for Information Interchange and is pronounced with a hard “C” sound, like ask-ee. As a standard, it was first adopted in 1963 and quickly became widely used throughout the computing world. It is used to define a set of characters that can be displayed by a computer on a screen and includes some control characters that have special functions.
Basic ASCII uses seven bits to define each letter, which means it can have up to 128 specific identifiers, power 27. This size was chosen based on the common building block of computation, the byte, which consists of eight bits. The eighth bit was often set aside for error-checking functions, leaving seven remaining for a character set.
There are 33 codes in ASCII that are used to represent things other than specific characters. The first 32 (0-31) represent anything from a bell ring, to a linefeed command, to the start of a header. The final code, 127, represents a backspace. Beyond the first 31 bits are the printable characters. Bits 48-57 represent numeric digits, bits 65-90 are uppercase letters, and bits 97-122 are lowercase letters. The rest of the bits are punctuation symbols, math symbols, and other symbols like the pipe and tilde.
ASCII started out in theory as a simpler character set, using six bits rather than seven. Eventually it was decided that adding lowercase letters, punctuation, and control characters would greatly improve its usefulness. Not long after its adoption, there was much discussion about possible replacements and adaptations of the code to incorporate non-English and even non-Roman characters. An ISO standard (646) was created as early as 1972 in an attempt to allow for a wider range of characters. However, a number of problems existed with ISO-646, which have been left on the back burner.
The current main contender for replacing this standard is the Unicode character set. Allows you to map essentially unlimited characters by using collections of bytes to represent a character, rather than a single byte. The first byte of all Unicode standards remains dedicated to the ASCII character set, however, to preserve backward compatibility.
The standard is sometimes also discussed in reference to ASCII art. Describes the use of the basic character set to create visual approximations of images.
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