Section One: Before the Great Dark Cloud.
Part I: The Intel 4004 (1972)
The first single chip CPU was the Intel 4004, a 4-bit processor meant for
a calculator. It processed data in 4 bits, but its instructions were
8 bits long. Internally, it featured four 12 bit(?) registers which acted as
an internal evaluation stack. The Stack Pointer pointed to one of these
registers, not a memory location (only CALL and RET instructions operated on
the Stack Pointer). There were also sixteen 4-bit (or eight 8-bit) general
The 4004 had 46 instructions. Intel created an 8-bit version of this, the
8008 (intended for a terminal controller).
[for additional information, see Appendix B]
Part II: The Intel 4040 and 8080
The 4040 was compatible with the 4004 instruction set - the 4040 had 60
instructions, which included the 46 4004 instructions. The 8080 was similar to
the 4040, except being 8 bits wide.
The 8080 had a 16 bit address bus, and an 8 bit data bus. Internally it
had seven 8 bit registers (six which could also be combined as three 16 bit
registers), a 16 bit stack pointer (the stack was stored in memory, not in an
internal register set), and 16 bit program counter. It also had several I/O
ports - 256 of them, so I/O devices could be hooked up without taking away or
interfering with the addressing space.
Appearing in IEEE Computer 1972:
COMPUTER ON A CHIP
Intel has introduced an integrated CPU complete with
a 4-bit parallel adder, sixteen 4-bit registers, an accumula-
tor and a push-down stack on one chip. It's one of a
family of four new ICs which comprise the MCS-4 micro
computer system--the first system to bring the power and
flexibility of a dedicated general-purpose computer at low
cost in as few as two dual in-line packages.
MSC-4 systems provide complete computing and con-
trol functions for test systems, data terminals, billing
machines, measuring systems, numeric control systems
and process control systems.
The heart of any MSC-4 system is a Type 4004 CPU,
which incudes a set of 45 instructions. Adding one or
more Type 4001 ROMs for program storage and data
tables gives a fully functioning micro-programmed com-
puter. Add Type 4002 RAMs for read-write memory and
Type 4003 registers to expand the output ports.
Using no curcuitry other than ICs from this family of
four, a system with 4096 8-bit bytes of ROM storage and
5120 bits of RAM storage can be created. For rapid
turn-around or only a few systems, Intel's erasable and
re-programmable ROM, Type 1701, may be substituted
for the Type 4001 mask-programmed ROM.
MCS-4 systems interface easily with switches, key-
boards, displays, teletypewriters, printers, readers, A-D
converters and other popular peripherals. For further
information, circle the reader service card 87 or call Intel
at (408) 246-7501.
Circle 87 on Reader Service Card