CHAPTER 1
Introduction
In 1971, Intel Corporation introduced the first microcomputer on
a chip, the Intel 4004. Although the 4004 was truly not a self-con-
tained computer on a single Large-Scale-Integration (LSI) chip, it
contained a great deal of logic associated with computer central
processing unit implementation. One LSI chip replaced hundreds of
circuits that were to be found in conventional minicomputers at the
time. Although the 46-instruction repertoire was not large, it was
adequate for control applications which required decision making
that could not easily be implemented in programmable-logic arrays
and in which extensive mathematical processing was not required.
The 4004 handled data 4 bits at a time and could perform 100,000
additions of two 4-bit operands per second.
The next generation of microprocessors from Intel retained the
PMOS (P-channel metal-oxide semiconductor) fabrication tech-
niques of the 4004, but offered an 8-bit wide
data bus
and a larger
instruction repertoire of 48 instructions. Designated the 8008, the
microprocessor had a faster instruction cycle time than the 4004 as
data for both instruction execution and decoding and for operands
could be handled in 8-bit slices. In addition, the 8008 could address
16,384 memory locations of 8 bits each, contained seven 8-bit regis-
ters, had memory stack capability, and had a single-level interrupt
capability. The 8008 could perform approximately 80,000 additions
of two 8-bit operands per second. The instruction set of the 8008 was
not compatible with the 4004.
The 8008 and 4004 had achieved widespread usage through the
electronics industry in a very short time after their introduction,
primarily because there was little else available in the way of micro-
processors. To achieve compatibility with the 8008 insofar as instruc-
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