12-bit computing

Before the widespread adoption of ASCII in the late 1960s, six-bit character codes were common and a 12-bit word, which could hold two characters, was a convenient size. This also made it useful for storing a single decimal digit along with a sign. Possibly the best-known 12-bit CPU is the PDP-8 and its relatives, such as the Intersil 6100 microprocessor produced in various forms from August 1963 to mid-1990. Many analog to digital converters (ADCs) have a 12-bit resolution. Some PIC microcontrollers use a 12-bit word size.

12 binary digits, or 3 nibbles (a 'tribble'), have 4096 (10000 octal, 1000 hexadecimal) distinct combinations. Hence, a microprocessor with 12-bit memory addresses can directly access 4096 words (4 kW) of word-addressable memory. IBM System/360 instruction formats use a 12-bit displacement field which, added to the contents of a base register, can address 4096 bytes of memory in a region that begins at the address in the base register.

List of 12-bit computer systems

 * Digital Equipment Corporation
 * PDP-5
 * PDP-8
 * DECmate, a personal computer based on the Intersil 6100
 * PDP-12
 * PDP-14
 * Ford EEC I automotive engine control unit
 * Toshiba TLCS-12 microprocessor
 * Intersil IM6100 microprocessor (PDP-8-compatible)
 * Control Data Corporation
 * CDC 160 series computers
 * CDC 6600 - Peripheral Processor (PP)
 * National Cash Register NCR 315
 * Scientific Data Systems SDS 92
 * Nuclear Data, Inc. ND812
 * PC12 minicomputer
 * Ferranti Argus
 * LINC, later commercialized by DEC as the LINC-8
 * Electronic Arrays 9002 (12-bit addressing but 8-bit byte)