The Intel 4004 was a 4-bit central processing unit built on a single integrated circuit and announced by Intel in November 1971. It was the CPU member of a four-chip family known as the MCS-4. The Computer History Museum’s Intel 4004 oral history panel, which gathered the surviving members of the design team, records that the MCS-4 chipset announced in November 1971 is now recognized by the industry as the first commercial microprocessor.
The project began as a contract from the Japanese calculator company Busicom, which approached Intel for a set of custom chips for a desktop calculator. As Ted Hoff and Stan Mazor describe in their Computer History Museum oral history, Hoff, then manager of Applications Research, proposed redesigning the custom calculator logic into a general-purpose solution organized around a 4-bit CPU rather than a large set of fixed-function chips. Mazor, recruited from Fairchild, helped configure the architecture, working with Busicom’s engineer Masatoshi Shima.
Turning that architecture into working silicon fell to Federico Faggin, who joined Intel in 1970 and applied the MOS silicon-gate process he had developed. The same oral histories credit Faggin with converting the team’s concept into four MOS silicon-gate integrated circuits that became the first commercial microprocessor chip set. The silicon-gate process was the key enabler: it allowed enough transistors at enough speed on one die to make a single-chip CPU practical.
The 4004 first ran inside a Busicom 141-PF printing calculator. Recognizing the broader potential of a programmable chip, Intel negotiated to reacquire the general rights from Busicom and began selling the 4004 as a stand-alone product, advertising “a new era of integrated electronics.” That commercial availability is what separates the 4004 from earlier one-off integrated processors: any engineer could buy one and program it.
Though modest by later standards, with a 4-bit data path and a clock measured in hundreds of kilohertz, the 4004 established the template that every later Intel processor followed. It led directly to the 8-bit 8008 and 8080 and, through Faggin’s later work at Zilog, to the Z80. The architectural idea it proved, that an entire CPU could live on one mass-produced chip, is the foundation of the microprocessor era.