12-bit computing

In computer architecture, 12-bit integers, memory addresses, or other data units are those that are 12 bits (1.5 octets) wide. Also, 12-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 best-known 12-bit CPU is the PDP-8 and its relatives, such as the Intersil 6100 microprocessor produced in various incarnations 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. At a time when six-bit character codes were common a 12-bit word, which could hold two characters, was a convenient size. 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.

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
• Intersil IM6100 microprocessor (PDP-8-compatible)
• Control Data Corporation
  • CDC 6600 - Peripheral Processor (PP)
  • CDC 160 series computers
• National Cash Register NCR 315
• Scientific Data Systems SDS 92
• Ford Motor Company EEC I Automotive engine control unit
• PC12 minicomputer
• Ferranti Argus
• LINC, later commercialized by DEC as the LINC-8

See also

• FAT12, a file system with 12-bit wide cluster entries

References

• DIGITAL Computing Timeline: 12-bit architecture