The total microprocessor population has passed 10 billion - two for every human being
After a prolonged and tempestuous adolescence, the microprocessor, possibly the most important invention of the 20th century, has reached the age of 25. No bigger than a fingernail, these miniaturised computers are the electronic brains inside today's space vehicles, video games, PCs and kitchen toasters.

Each tiny silicon "chip" has the computing power of a roomful of old-fashioned mainframes and 100 times that of a PC of a decade ago. Their total population has passed 10 billion - two for every human beings.

A chip is not simply a new product: it is a technology that inserts intelligence into products. The BMW 325, for example, contains about 100 chips; the average home entertainment centre, two dozen.

If you were to home in on a microchip through powerful magnification, it would be like landing by parachute in a city with myriad pathways connecting tall buildings, parks and racecourses - here a memory bank, there an instruction cache capable of handling 300 million instructions per second. A single speck of dust entering the manufacturing process would mimic the destruction caused by an asteroid hitting the city.

No other invention has evolved so fast or generated so much wealth, power - and bitter rivalry. Whereas the industrial revolution was characterised by a 50-fold increase in production that irrevocably changed society, the microprocessor has already improved its performance 1,000 times - the equivalent of an industrial revolution every two-and-a-half years, according to Michael Malone, author of The Microprocessor: A Biography (recently published by Springer at pounds 19.50).

The chips are down for mankind

Chips are unlikely to take over the world while there still exists one human with hammer. But they have already put human intelligence to shame: the most costly patent infringement litigation of the electronic era - in which the industry giant Intel challenged the upstart Advanced Micro Devices's right to clone (copy) its products - ended this year after six years, having cost nearly $250m (pounds 160m), and at a time when both companies were working on devices three generations more advanced and a thousand times more powerful. An exasperated judge finally ordered them to settle.

The microprocessor, for all its intelligence, is in some ways just like any other invention. Apparently several inventors thought of it simultaneously, and now there is litigation over rights and squabbling over credit.

Hitherto, historians have awarded the invention to Intel's 12th employee, Ted Hoff, a brilliant ex-Stanford research associate who was the first to design a general-purpose calculator on a single chip.

Ever heard of Federico Faggin?

Busicom, the Japanese calculator company that Intel was supplying, at first showed no interest. The design languished, until Federico Faggin completed its development. When Faggin left Intel in 1974, (to found his own company, Zilog) his name disappeared from Intel company history. But his wife Elvia has made it a personal crusade - writing indefatigably to the media - to redress what she sees as an injustice. History will probably credit Hoff as inventor and Faggin as creator.

In 1971, Busicom signed away rights to Intel's chips for all uses except calculators. The company could have owned the microprocessor. The winners were the purchasers of Intel's shares - 100 bought for $2,350 (pounds 1,500) in 1968 would have grown to $500,000 today.

Tomorrow? The bioprocessor - the growing, thinking, learning, organic chip that mimics the human brain. One wonders whether it will develop a taste for litigation