7-bit
What is 7-bit?
Standard ASCII uses exactly 7 binary digits per character, yielding 2^7 = 128 possible values (decimal 0-127). Those 128 slots cover 33 control characters, the space character, 52 uppercase and lowercase letters, 10 digits, and 32 punctuation and symbol characters.
The 7-bit constraint was deliberate: early teletype circuits transmitted 7 data bits plus 1 parity bit per byte. When the industry moved to clean 8-bit channels, that spare bit enabled extended ASCII encodings like CP437 and ISO-8859-1 to add another 128 characters. Watch out: many "ASCII" references actually mean an 8-bit superset, not the original 7-bit standard.
The 7-bit constraint was deliberate: early teletype circuits transmitted 7 data bits plus 1 parity bit per byte. When the industry moved to clean 8-bit channels, that spare bit enabled extended ASCII encodings like CP437 and ISO-8859-1 to add another 128 characters. Watch out: many "ASCII" references actually mean an 8-bit superset, not the original 7-bit standard.