The Intel 4004 is a 4-bit central processing unit (CPU) released by Intel Corporation in 1971. It was the first commercially available microprocessor and the first in a long line of Intel CPUs. The chip design, implemented with the MOS silicon gate technology, started in April 1970 and was created by Federico Faggin who led the project from beginning to completion in 1971. Marcian Hoff formulated and led the architectural proposal in 1969, and Masatoshi Shima contributed to the architecture and later to the logic design. The first commercial sale of the fully operational 4004 occurred in March 1971 to Busicom Corp. of Japan for its 141-PF electronic calculator, for which it was originally designed and built as a custom chip.

In November 1971, with the prophetic ad "Announcing a new era in integrated electronics", the 4004 was made commercially available to the general market. The 4004 was the first commercially available monolithic processor, fully integrated in one small chip. Such a feat of integration was made possible by the use of the then-new silicon gate technology for integrated circuits, originally developed by Faggin (with Tom Klein) at Fairchild Semiconductor in 1968, which allowed twice the number of random-logic transistors and an increase in speed by a factor of five compared to the incumbent MOS (metal–oxide–semiconductor) aluminum gate technology.

More Info: