18-bit computing
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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.
The IBM 7700 Data Acquisition System was an 18-bit computer.