Intel 4004 - detail

Strictly seen, the i4004 doesn't exist. Intel developped for his customer Busicom a chip-set, called the "MCS-4". It consists of these components:

4001 ROM + 4Bit I/O
4002 RAM + 4Bit O
4003 shiftregister
4004 CPU

The prefix-letters indicate the package: C is ceramic, P is plastic. Layout of the chips is choosen that 10 of the pins may connected directly parallel. Two of them are chip-select for the memories and 4 are I/O ports. Without additional decoding hardware it is possible to connect up to four 4002 RAMs and four 4001 ROMs to the 4004-CPU. The 4003 shift-register can be used as output-expander.