National Semiconductor PACE

National Semiconductor's IPC-16A/520 PACE, short for "Processing and Control Element", was the first commercial[lower-alpha 1] single-chip 16-bit microprocessor. PACE had four general-purpose accumulators, with an instruction set architecture loosely based on the earlier IMP-16 architecture, which in turn had been inspired by the Data General Nova minicomputer.

National Semiconductor PACE die (IPC-16A/500)

PACE was slightly faster than the IMP-16, and offered a "byte mode" for more convenient processing of 8-bit data. Some PACE instructions were restricted to operation on only the first accumulator, AC0, rather than allowing use of any accumulator as on the IMP-16.

The PACE was followed by the INS8900, which had the same architecture but was implemented in NMOS for easier electrical interfacing.

Notes
  1. McDonnell Douglas produced a classified military 16-bit processor called the "Actron" around 1973.

References
  • IPC-16A PACE, National Semiconductor data sheet, Bitsavers (2018-01-06)
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