The Intel 4004 began in April 1969, when Japanese calculator maker Busicom asked Intel, then a small memory-chip startup, to build chips for a programmable desktop calculator to compete with the Olivetti Programma 101, which stored data as acoustic pulses in magnetostriction wire. Busicom’s engineers wanted seven custom chips. Marcian Ted Hoff, Intel employee number 12, saw that Intel lacked the staff and that the wiring would be too costly, and proposed four chips instead: a central processor, ROM, RAM and an input-output chip, with software telling the hardware what to do. Busicom agreed. Stanley Mazor joined to help write an interpreter, Busicom engineer Masatoshi Shima suggested an interrupt pin, and to meet the price the processor was squeezed into a 16-pin package by multiplexing addresses and data across the same pins.

When Shima returned in early 1970 he found the chip design had stalled, because Hoff and Mazor were architects, not silicon designers. Intel hired Federico Faggin in April 1970. Using the MOS silicon gate technology he had pioneered, plus buried contacts and bootstrap loads, he doubled density and made the chip five times faster than aluminum-gate designs, working 70 to 80 hour weeks while Shima stayed six months. The first batch in December 1970 was dead because the fab skipped the buried contact step; the January 1971 batch worked. With Busicom struggling in a price war, Faggin pushed Bob Noyce to forgive the $60,000 Busicom owed in exchange for rights to sell the chip for non-calculator uses, and marketing head Ed Gelbach launched it as the MCS-4 in November 1971.

• Intel executives feared selling a processor would drive away the computer makers who bought its memory chips.
• The 4004 had 2,300 transistors and sold for around $60, ending up in bottle loaders, arcade games, microwave ovens and traffic lights.
• Texas Instruments’ earlier TMS0100 had its program fixed by a photomask, and the F-14 Central Air Data Computer was multi-chip and classified until 1998.
• Faggin etched his initials, FF, into the corner of the silicon die.
• A programmer recently booted a stripped-down Debian Linux on an emulated 4004, which took five days.