ASCII

ASCII (American Standard Code for Information Interchange, pronounced “ass-key”) is a character encoding that maps 128 symbols to the integers 0-127. Defined in 1963 and standardised internationally as ISO/IEC 646 in 1972.

Coverage:

• 0-31: control characters (NUL, newline, carriage return, tab, escape, bell)
• 32-47: punctuation and symbols (space, !, ", #, $, %, etc.)
• 48-57: digits 0-9
• 58-64: more punctuation (:, ;, <, =, >, ?, @)
• 65-90: uppercase A-Z
• 97-122: lowercase a-z
• 127: DEL

ASCII fits in 7 bits, which is why old serial protocols and telegraph systems used 7-bit transmission. The 8th bit became the parity bit. Modern systems use 8 bits per character; the upper 128 values (128-255) are interpreted differently depending on the encoding chosen (Latin-1, Windows-1252, etc.).

UTF-8 is backward-compatible with ASCII — any ASCII text is a valid UTF-8 file with identical bytes. That compatibility is one of the main reasons UTF-8 won the Unicode encoding wars.