National Semiconductor

National Semiconductor

National Semiconductor was an American semiconductor manufacturer, that specialized in analog devices and subsystems,formerly headquartered in Santa Clara, California, USA. The products of National Semiconductor included power management circuits, display drivers, audio and operational amplifiers,...

's IPC-16A/520 PACE, short for "Processing and Control Element", was the first commercial single-chip 16-bit microprocessor

Microprocessor

A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...

. PACE had four general-purpose accumulators, with an instruction set architecture loosely based on the earlier IMP-16

IMP-16

The IMP-16, by National Semiconductor, was the first multi-chip 16-bit microprocessor. It consisted of five PMOS integrated circuits: four four-bit RALU chips providing the data path, and one CROM providing control sequencing and microcode storage.The IMP-16 provided four 16-bit accumulators,...

 architecture, which in turn had been inspired by the Data General Nova

Data General Nova

The Data General Nova was a popular 16-bit minicomputer built by the American company Data General starting in 1969. The Nova was packaged into a single rack mount case and had enough power to do most simple computing tasks. The Nova became popular in science laboratories around the world, and...

minicomputer.

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.