Forty years of the microprocessor

Forty years ago today, a magazine advert proclaimed the arrival of the Intel 4004, an integrated circuit that combined enough components to form a self-contained processor on a single chip for the first time. The microprocessor was born.

Follow the link to see V3's microprocessor timeline.

As with many great innovations, controversy surrounds who actually invented the microprocessor, but Intel's 4004 was the first chip to become commercially available to anyone that might wish to build something with it, a move that would quickly lead to the birth of the microcomputer industry.

In fact, as Intel has pointed out, it was the company's expertise in silicon manufacturing technology that enabled it to produce a working chip where others with the same idea had failed, and staying at the cutting edge of manufacturing process technology continues to be a key goal for Intel.

The 4004 was produced in 1971 in response to an order from Japanese firm Busicom to drive a new electronic calculator, but Intel decided to produce a general-purpose solution that could be programmed for other tasks, rather than build a single-purpose dedicated set of circuits.

With just 2,300 transistors, the 4004 seems incredibly basic compared to the latest Intel Core processors that are approaching a billion transistors on a single chip, but the basic elements of today's CPUs can be seen in the design of the 4004.

The chip featured a 4-bit bus through which it communicated with the RAM, ROM and I/O components that Intel designed as a complete chipset to fulfil the Busicom contract.

Programmers were somewhat limited in what they could accomplish with the 4004; it could address no more than 4KB of program memory (ROM) and a maximum 1,280 words of 4-bit data memory (RAM).

However, it should be noted that early products like the 4004 were viewed at the time as solutions for process control, to be embedded into devices such as calculators, printers and other equipment as a controller rather than to produce a general-purpose programmable computer.

Intel followed up the 4004 with the 8008, the first 8-bit microprocessor to come to market in 1972. This could address up to 16KB of memory, and powered some very early microcomputers, despite its limitations.

Microprocessors and microcomputers really started to take off with the launch of Intel's 8080 chip in 1974. With a memory space of 64KB and a clock speed up to 2MHz, this set the template for many 8-bit processors that followed, especially the Zilog Z80, which was software compatible with the 8080.

The 8080 formed the basis of the legendary Altair 8800, one of the first personal computers, which was sold as a kit for hobbyists to build themselves.