In computer architecture, 18-bit integers, memory addresses, or other data units are those that are 18 bits (2.25 octets) wide. Also, 18-bit CPU and ALU architectures are those that are based on registers, address buses, or data buses of that size.
|Computer architecture bit widths|
|Binary floating-point precision|
|Decimal floating-point precision|
18 bits was a common word size for smaller computers in the 1960s, when large computers often used 36 bit words and 6-bit character sets were the norm. There were also 18-bit teletypes experimented with in the 1940s.
Example computer architectures
The BCL Molecular 18 was a group of systems designed and manufactured in the UK in the 1970s and 1980s.
The flying-spot store digital memory in the first experimental electronic switching systems used nine plates of optical memory that were read and written two bits at a time, producing a word size of 18 bits.
18-bit machines use a variety of character encodings.
The DEC Radix-50, called Radix 508 format, packs three characters plus two bits in each 18-bit word.
The Teletype packs three characters in each 18-bit word; each character a 5-bit Baudot code and an upper-case bit.
- "Linking Loader". PDP-9 Utility Programs--Advanced Software System--Programmer's Reference Manual (PDF). Maynard, Massachusetts: Digital Equipment Corporation. 1968. p. A1-1. Archived (PDF) from the original on January 25, 2019.
- PDP-7 Symbolic Assembler Programming Manual (PDF). Maynard, Massachusetts: Digital Equipment Corporation. 1965. pp. 6, 38–39. Archived (PDF) from the original on May 23, 2017. Retrieved June 18, 2015.