In November 1971 Intel announced a product that few people at the time considered revolutionary: a chip called the 4004, which contained the entire central processing unit of a computer. It was the first commercial microprocessor. Almost every digital device we use today, from the laptop to the washing machine, descends from that idea.
An order for a calculator
It all began in 1969 with a Japanese calculator company, Busicom, which asked Intel, then a young company specialising in memory chips, to produce the chips for a new family of desktop calculators. Busicom's original design called for numerous custom chips, each dedicated to a specific function.
Ted Hoff's idea
Marcian "Ted" Hoff, an Intel engineer, felt the design was too complex and expensive. He proposed an alternative: instead of many specialised chips, a small general-purpose, programmable processor, alongside memory chips. The calculator's functions would be implemented by the program held in read-only memory, not by the circuits. Stanley Mazor helped define the architecture and the instruction set.
It was a fundamental change of perspective. A chip of this kind could serve the calculator, but also any other application: you only had to change the program.
Federico Faggin and the implementation
The architecture was defined, but someone had to turn it into a working chip. In 1970 Intel hired Federico Faggin, a physicist born in Vicenza who had worked in Italy and then at Fairchild Semiconductor in California.
At Fairchild, Faggin had developed silicon gate technology, in which the control terminal of the transistors is made of polycrystalline silicon instead of metal. This technology allowed smaller, faster and denser transistors: exactly what was needed to put an entire processor on a single chip.
Faggin led the logic and circuit design of the 4004 and the family of chips that went with it, working closely with Masatoshi Shima, a Busicom engineer. He also developed new design techniques to overcome the problems that arose. He etched his initials, "FF", onto the chip.
The MCS-4 family
The 4004 did not work alone. It was part of a set of four chips:
| Chip | Function |
|---|---|
| 4001 | Read-only memory (ROM) for the program |
| 4002 | Random-access memory (RAM) for data |
| 4003 | Shift register for input and output |
| 4004 | 4-bit central processor |
Features of the 4004
The 4004 was a 4-bit processor: it handled data in groups of four binary digits, enough to represent one decimal digit, a natural fit for a calculator. It contained about 2,300 transistors and was made with a 10-micrometre process. A modern processor contains billions of transistors, with dimensions measured in nanometres.
Buying back the rights
Initially Busicom held exclusive rights to the chip. Faggin and others at Intel realised that the 4004 could have a much wider market. Intel renegotiated the agreement with Busicom, which was in financial difficulty at the time, obtaining the right to sell the chip to other customers for applications other than calculators, in exchange for better financial terms for Busicom.
In November 1971 Intel announced the product with an advertisement that spoke of a new era of integrated electronics.
After the 4004
The 4004 was quickly followed by more powerful processors:
- 8008 (1972), Intel's first 8-bit microprocessor.
- 8080 (1974), much more powerful, used in the Altair 8800, the kit computer that set off the personal computer revolution.
- From here descend the 8086 and 8088, the latter chosen in 1981 for the IBM PC, which gave rise to the x86 architecture still dominant in desktop computers and servers today.
Faggin left Intel in 1974 and founded Zilog, which produced the Z80, an 8-bit processor compatible with the 8080 that was hugely successful in home computers and industrial systems.
Why the microprocessor was decisive
The importance of the 4004 does not lie in its performance, modest even for the time. It lies in the model it introduced:
- One standard component for many uses. Instead of designing different circuits for each product, you could use the same chip and change the software.
- Falling costs. Produced in large volumes, the microprocessor became ever cheaper.
- Computers everywhere. With a processor on a chip, computing power could be put into instruments, cars, household appliances and toys.
This is the shift that moved the value of many products from hardware to software, a trend that embedded systems developers still see every day.
In short
- The Intel 4004, announced in November 1971, was the first commercial microprocessor, born from an order placed by the Japanese company Busicom.
- Ted Hoff proposed the idea of a general-purpose programmable processor; Stanley Mazor contributed to the architecture.
- Federico Faggin led the chip's design using silicon gate technology, working with Masatoshi Shima.
- The 4004 was a 4-bit chip with about 2,300 transistors; Intel's processor line down to the x86 architecture descends from it.
