ASCII
ASCII - quick reference
ASCII (American Standard Code for Information Interchange) maps 128 characters to the integers 0-127 using 7 bits. Published as ASA X3.4 in 1963 and finalized as ANSI X3.4-1986, it assigns 33 control codes, a space, 26 uppercase and 26 lowercase Latin letters, 10 digits, and 32 punctuation marks.
ASCII's design reflects 1960s constraints. The committee chose 7 bits (not 8) because teletype links used the 8th bit for parity checking. Letter codes were arranged so that bit 5 toggles case and bit 6 separates letters from control codes. These bit-level tricks made hardware implementation cheap. See the ASCII timeline for the full history, the complete table for all 128 values, and our FAQ for common questions.
ASCII's design reflects 1960s constraints. The committee chose 7 bits (not 8) because teletype links used the 8th bit for parity checking. Letter codes were arranged so that bit 5 toggles case and bit 6 separates letters from control codes. These bit-level tricks made hardware implementation cheap. See the ASCII timeline for the full history, the complete table for all 128 values, and our FAQ for common questions.