IMP-16
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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 (Register and ALU) providing the data path, and one CROM (Control and ROM) providing control sequencing and microcode storage.
The IMP-16 provided four 16-bit accumulators, two of which could be used as index registers. The instruction set architecture was similar to that of the Data General Nova.
The IMP-16 was later superseded by National Semiconductor's PACE and INS8900 single-chip 16-bit microprocessors, which had a similar architecture but were not binary compatible.
References
- National Semiconductor (1973). IMP-16 Programming and Assembler Manual.