The Intel 4004 processor gets much attention for being the ‘first’ processor, however, there were others. The Rockwell PPS-4 was introduced in 1972, making it one of only 4 processors of the time (IMP-16 from National Semiconductor, Intel 8008 and Intel 4004 being the others.
The original PPS-4 came in a 42 pin Quad Inline package, compared to the 4004s somewhat limiting 16 pins. A complete system could be built using 3 chips, a 10660 (later the 12660) PPS-4 processor, a ROM, and a clock generator (10706). The PPS-4 was manufactured on a metal gate process (vs the silicon gate process of the 4004). It required a single -17VDC power supply and ran at 256KHz.
In 1975 Rockwell introduced the PPS-4/2 (aka the 11660). The ‘/2’ denoting the 2 chip version of the PPS-4. The clock generator was now moved onto the processor itself, and a memory/IO chip (part # A17xx) that provided 2048×8 bits of ROM 128×4 bits of RAM and 16 1 bit I/O ports. Clock speed was 200KHz, slightly less than that of the 3 chip PPS-4.
Rockwell was not done with the PPS-4. In 1976 they released the PPS-4/1, which was a single chip microcomputer version, integrating ROM onto the processor so that a system could be built with one chip. The standard version (the MM76) had 64×8 bits of ROM and 48×4 bits of RAM. Clock frequency could range from 40KHz to a blistering 120KHz. The PPS-4/1 was compatible with peripherals of the newly released PPS-8 as well. Additional versions were made including:
MM75: Reduced I/O 28 pin version
MM76E: Extended memory 1024x8bits of ROM
MM76C: Included a high speed counter and expanded I/O in a 52 pin package (140KHz max speed)
MM76D: Includes a ADC 52 pin package
MM76L/EL: Low voltage/low power version (-11 – -6.4 volts vs -15 of the standard parts)
MM77: 1344×8 ROM 96×4 RAM
MM78: 2048×8 bit ROM 128×4 RAM
A7699: Development version without on board ROM – requires external clocking
A7698: Development version without on board ROM – Can use internal clock
B769x: Development version for the MM76L/EL Low power versions
Unlike the Intel MCS-4/40 the Rockwell PPS-4 and its derivatives continued to be made and used well into the late 1980’s