ASCII and EBCDIC codes

Both are alphanumeric codes: binary codes that represent letters, digits, punctuation marks and control characters so that text can be stored and sent by digital systems.

ASCII

• American Standard Code for Information Interchange.
• A 7-bit code, so it has $2^7 = 128$ characters (0–127); often stored in 8 bits with the MSB as 0 or as a parity bit.
• Codes 0–31 and 127 are control characters (e.g. LF = 0AH, CR = 0DH); 32–126 are printable.
• Letters and digits are in order, which makes sorting easy.
• Examples: 'A' = 100 0001 (41H), 'a' = 110 0001 (61H), '0' = 011 0000 (30H), space = 20H.
• Used in PCs, keyboards, the internet and most modern systems.

EBCDIC

• Extended Binary Coded Decimal Interchange Code, developed by IBM.
• An 8-bit code, so up to $2^8 = 256$ characters.
• Based on BCD: the lower 4 bits of a digit are its BCD value and the upper 4 bits (zone) are 1111.
• Letters are not in one continuous block (gaps between I/J and R/S).
• Examples: 'A' = 1100 0001 (C1H), 'a' = 1000 0001 (81H), '0' = 1111 0000 (F0H), '9' = F9H.
• Used mainly in IBM mainframes.