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IMP-4 - National Semiconductor
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National IMP-4
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Developer National Semiconductor
Manufacturer National Semiconductor
Production March, 1973-1977
Release date March, 1973
Architecture 4-bit bit-slice
Word size 4 bit
0.5 octets
1 nibbles
Process 10 μm
10,000 nm
0.01 mm
Technology pMOS
Clock 500 kHz-750 kHz
Package DIP24

The National IMP-4 (originally National GPC/P) was a family of multi-chip 4-bit bit-slice microprocessor developed by National Semiconductor and introduced in 1973. Units could be combined to implement systems with 4 to 32-bit words. The IMP-8 and IMP-16 families were made using the IMP-4 logic. The IMP-4 had 2 chips: a control unit and an ALU, some systems used the RALU with custom control circuitry. The RALU was the first bit-slice microprocessor - predating both the 3000 and the am2900.

2nd sources[edit]

Rockwel was the only 2nd source for the IMP-4 series. Some USSR clones are known to exist.


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Family Members
IMP-4A/520 IMP-4A/420 Bundled Kit, CROM + RALU
IMP-4A/521 IMP-4A/421 Control and Read-only Memory (CROM)
IMP-00A/520 IMP-00A/420 Register and Arithmetic Logic Unit (RALU)

Text document with shapes.svg This article is still a stub and needs your attention. You can help improve this article by editing this page and adding the missing information.
designerNational Semiconductor +
full page namenational semiconductor/imp-4 +
instance ofintegrated circuit family +
main designerNational Semiconductor +
manufacturerNational Semiconductor +
nameNational IMP-4 +
packageDIP24 +
process10,000 nm (10 μm, 0.01 mm) +
technologypMOS +
word size4 bit (0.5 octets, 1 nibbles) +