18-bit computing

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 central processing unit (CPU) and arithmetic logic unit (ALU) architectures are those that are based on registers, address buses, or data buses of that size.

Possibly the most well-known 18-bit computer architectures are the PDP-1, PDP-4, PDP-7, PDP-9 and PDP-15 minicomputers produced by Digital Equipment Corporation from 1960 to 1975. UNIVAC also produced a number of 18-bit computers, including the UNIVAC 418 and several military systems.

18 binary digits have 262144 (1000000 octal, 40000 hexadecimal) unique combinations.

References

• DIGITAL Computing Timelime: 18-bit architecture
• Architectural Evolution in DEC’s 18b Computers, Bob Supnik, 2006.