INTRODUCTION The Intel 4004 was a 4-bit central processing unit (CPU) released by Intel Corporation in 1971 by Intel engineers Federico Faggin, Ted Hoff, and Stanley Mazor. It was the first complete CPU on one chip, and also the first commercially available microprocessor.This was made possible by the use of then-new silicon gate technology allowing a higher number of transistors and a faster speed than was possible before.The Intel 4004 chip took the integrated circuit down one step further by placing all the parts that made a computer think (i.e. central processing unit, memory, input and output controls) on one small chip.
Picture of Federico Faggins initials etched on the edge of the 4004
FEATURES Maximum clock speed 740 kHz 8 clock cycles / instruction cycle Instruction execution time 1 or 2 instruction cycles (10.8 or 21.6 µs), 46300 to 92600 instructions per second It uses a single multiplexed 4-bit bus for transferring: 12-bit addresses 8-bit instructions 4-bit data words Instruction set contained 46 instructions (of which 41 were 8 bits wide and 5 were 16 bits wide) Register set contained 16 registers of 4 bits each Internal subroutine stack 3 levels deep.
ADDRESSING MODESImmediate (4 and 8-bit data).Register indirect. Register indirect can access data onlywithin current ROM.Memory direct.Register (4-bit).
INSTRUCTION SET4004 instruction set consists of 46 instructions: Data moving insrtuctions. Arithmetic - add, subtract, increment, decrement. Logic - rotate. Control transfer - conditional (limited to current ROM), unconditional, call subroutine and return from subroutine. Input/Output instructions. Other - carry flag operations, decimal adjust, etc. Instruction length can be one or two bytes