National Semiconductor PACE

National Semiconductor's IPC-16A PACE, short for "Processing and Control Element", was the first commercial single-chip 16-bitmicroprocessor, announced in late 1974. It was a single-chip implementation of their early 1973 five-chip IMP-16 architecture, which in turn had been inspired by the Data General Nova minicomputer. To the basic IMP-16, PACE added a new operational mode, "byte mode", which was useful for working with 8-bit data like ASCII text.

Implemented in pMOS, as was common for the era, PACE required three supply voltages and an external clock with enough signal to drive the internal logic. This was normally supplied by the STE chip. Most PACE systems also required the BTE chip to convert the higher internal voltage signals to TTL levels used by the rest of the system. Its multiplexed address and data pins also required additional logic.

Although National Semiconductor had second source agreements with Signetics and Rockwell Semiconductor, neither company produced the PACE design. The PACE was followed by the INS8900, which had the same architecture but was implemented in nMOS. This version made electrical interfacing easier and also fixed several bugs in the PACE logic and increased the speed by about 50%. By the time it was available, higher-performance 16-bit CPUs were appearing, and the company began to deemphasize sales of the line.