IEEE Spectrum September, 2016 - 50

haT OpEnEd ThE dOOr for the first
microprocessors, then, was the application
of MOS integrated circuits to computing.
The first computer to be fashioned out of MOSLSI chips was something called the d200, created
in 1967 by autonetics, a division of
north american aviation, located in
anaheim, Calif.
This compact, 24-bit generalpurpose computer was designed
for aviation and navigation. Its central processing unit was built from
24 MOS chips and benefitted from a
design technique called four-phase
logic, which used four separate clock
signals, each with a different on-off
pattern, or phase, to drive changes
in the states of the transistors, allow-

three ProUd Parents: Posing during
induction ceremonies for the National
Inventors Hall of Fame in 1996, Federico
Faggin, Marcian "Ted" Hoff Jr., and Stanley
Mazor [from left] show off the pioneering
microprocessor they created in the early
1970s, the Intel 4004.
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SEP 2016

NORTh AMERICAN

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ing the circuitry to be substantially simplified. Weighing only a few
kilograms, the computer was used for guidance on the poseidon
submarine-launched ballistic missile and for fuel management on
the B-1 bomber. It was even considered for the space shuttle.
The d200 was followed shortly by another avionics computer that
contained three CpUs and used in total 28 chips: the Central air data
Computer, built by Garrett airesearch (now part of honeywell). The
computer, a flight-control system designed for the F-14 fighter, used the
Mp944 MOS-LSI chipset, which Garrett airesearch developed between
1968 and 1970. The 20-bit computer processed information from sensors and generated outputs for instrumentation and aircraft control.
The architecture of the F-14 computer was unusual. It had three
functional units operating in parallel: one for multiplication, one for
division, and one for special logic functions (which included clamping a value between upper and lower limits). Each functional unit was
composed of several different kinds of MOS chips, such as a read-only
memory (rOM) chip, which contained the data that determined how
the unit would operate; a data-steering chip; various arithmetic chips;
and a raM chip for temporary storage.
Because the F-14 computer was classified, few people ever knew
about the Mp944 chipset. But autonetics widely publicized its d200,
which then inspired an even more compact MOS-based computer:
the System IV. That computer was the brainchild of Lee Boysel, who
left Fairchild Semiconductor in 1968 to cofound Four-phase Systems,
naming his new company after autonetics' four-phase logic.
The CpU of the 24-bit System IV was constructed from as few as nine
MOS chips: three arithmetic-logic-unit (aLU) chips of a design dubbed
the aL1 (which performed arithmetic operations like adding and subtracting, along with logical operations like and, Or, and nOT), three
rOM chips, and three random-logic chips.
almost simultaneously, a Massachusetts-based startup called Viatron
Computer Systems got into the game. Just a year after its launch in
november 1967, the company announced its System 21, a 16-bit minicomputer with various accessories, all built from custom MOS chips.

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By the end of the 1960s, a single MOS integrated
circuit could contain 100 or more logic gates, each
containing multiple transistors, making the technology particularly attractive for building computers. These chips with their many components were
given the label LSI, for large-scale integration.
Engineers recognized that the increasing density of MOS transistors would eventually allow a
complete computer processor to be put on a single chip. But because MOS transistors were slower
than bipolar ones, a computer based on MOS chips
made sense only when relatively low performance
was required or when the apparatus had to be small
and lightweight-such as for data terminals, calculators, or avionics. So those were the kinds of
computing applications that ushered in the microprocessor revolution.
Most engineers today are under the impression
that the start of that revolution began in 1971 with
Intel's 4-bit 4004 and was immediately and logically followed by the company's 8-bit 8008 chip. In
fact, the story of the birth of the microprocessor is
far richer and more surprising. In particular, some
newly uncovered documents illuminate how a longforgotten chip-Texas Instruments' TMX 1795-beat
the Intel 8008 to become the first 8-bit microprocessor, only to slip into obscurity.

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Table of Contents for the Digital Edition of IEEE Spectrum September, 2016