The IT Facts

The Intel 4004 is a 4-bit central processing unit (CPU) released by Intel Corporation in 1971. It was the first commercially produced 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 delivery of a fully operational 4004 occurred in March 1971 to Busicom Corp. of Japan for its 141-PF printing calculator engineering prototype (now displayed in the Computer History Museum – Mountain View, Ca). This calculator for which the 4004 was originally designed and built as a custom chip was first commercially available in July 1971.

The 4004 was the first random logic circuit integrated in one chip using the MOS (metal–oxide–semiconductor) silicon gate technology (SGT). It was the most advanced integrated circuit (IC) design undertaken up until then. Hoff, head of Intel’s Application Research department, had formulated an architectural proposal consisting of a block architecture with an instruction set during 1969, while talking with Busicom engineers led by Shima and with the assistance of Stan Mazor. Hoff and Mazor were not MOS chip designers and did not participate in the actual design or development of the 4004.

The chip design was realized independently in the MOS department, different from Application Research. It could only be realized by a designer with deep knowledge of MOS process technology and of the new SGT. Faggin was hired at Intel in April 1970 from Fairchild Semiconductor to be the project leader and designer of the 4004 and he transferred to manufacturing a fully functional chip in March 1971. Faggin brought to Intel his mastery of the SGT that he had invented at Fairchild (in 1968) and used it to develop his novel methodology for random chip design that was key to making the first and all the early Intel microprocessors. Shima, representing Busicom, was engaged with Hoff and Mazor in the architectural phase during 1969 and he also assisted Faggin with the final logic design for 6 months in 1970.

In November 1971, with the prophetic advert "Announcing a new era in integrated electronics", the 4004 was made commercially available to the general market. The 4004 was the first monolithic processor, fully integrated in one small chip. Such a feat of integration was made possible by the use of the 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 aluminum gate technology. Faggin also invented the bootstrap load with silicon gate and the "buried contact", improving speed and circuit density compared with aluminum gate.

The 4004 microprocessor, the 4001 ROM, 4002 RAM, and 4003 Shift Register constituted the four chips in the Intel MCS-4 chip set. With these components, small computers with varying amounts of memory and I/O facilities could be built.