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British chip designer ARM will soon be 20 years old. Bill Thompson was there at the start.

During the 1980s I worked at Acorn Computers in Cambridge, helping to develop the in-house engineering systems that were used by designers to create computers like the Archimedes, the popular successor to the �鶹Լ�� Microcomputer that had made Acorn's name during the �鶹Լ�� Computer Literacy project.

The computer on my desk was a �鶹Լ�� Model "B" microcomputer with a whopping 32 kilobytes of memory and, I believe, a 10 megabyte hard drive.

When I had to write a program to calculate hours worked for my team I didn't use the BASIC language shipped with every �鶹Լ�� Computer, but wrote it instead using PostScript, the special programming language used to lay out documents on the very expensive Apple LaserWriter printer that we had on our floor, and got the printer to do the calculations I needed.

This printer not only had an astonishing one and half megabytes of memory - needed to cope with large documents - but used a Motorola 68000 processor, making it far more powerful than the aging 6502 in my desktop computer, so it was much faster.

At the time, however, there was far more excitement in the office about another sort of processor, one that had been developed by the research and development team inside Acorn: the Acorn RISC Machine, or ARM.

ARM chips were just starting to appear, and like everyone else in Acorn I spent a lot of my work time playing the marvellous "Lander" game that had been written to show off their speed and graphics capabilities.

"RISC" means "Reduced Instruction Set Computer", and describes an architectural approach that cuts down the complexity of the fundamental logical operations that the processor carries out in favour of the speedy execution of a smaller set of basic tasks, and the ARM chip marked a radical break with prevailing processor designs.

RISC chips have fewer transistors and simpler architectures, but they can be programmed to perform very efficiently. They also use a lot less power than more conventional processors, which makes them ideal for use in systems that either have limited power and should not overheat, like mobile phones.

This explains why ARM chips are now found in phones and mobile devices from Nokia, Samsung, Sony Ericsson and of course Apple.

Mobile power

Although ARM started within Acorn, it didn't stay there.

In November 1990 Acorn created a joint venture with Apple and chip manufacturer VLSI, and Advanced RISC Machines Ltd was created to develop the ARM architecture. Since then it has grown into the most successful British company to have emerged from Silicon Fen, with offices around the world and chips in billions of devices.

Part of the secret of ARM's success is that it doesn't actually make many processors itself. Instead it licenses its designs to other companies who then incorporate an "ARM core" in their own more complex processors, which they then manufacture themselves.

Their designs now fall into three groups, or profiles. Application, for general processing, real-time, and microcontroller, for the embedded systems found in many machines.

Anyone who wants to play with an ARM processor can get their hands on one very easily from mbed, an ARM research project that supplies an ARM Cortex microcontroller on a 40 PIN board with a USB interface and a variety of web-based support tools that let you write and compile programmes in C and C++.

Like the open source Arduino platform, it is designed to encourage exploration, learning and prototyping, with a large and growing web-based user community who share ideas and code.

And next week the mbed engineers are celebrating ARM's twentieth anniversary in an appropriately geeky way by running a robot racing competition using an .

In the 1990's most of us assumed that Acorn's main impact would prove to be the generation of people who sat down in front of the startup screen of a �鶹Լ�� Micro and grappled with a command line to type in their own BASIC programs.

But 20 years later it's the billions of ARM processor cores in smartphones and handheld computers around the world that are shaping our world.

ARM has become into one of the most important companies propelling us into the age of electronics, and has shown remarkable skill in navigating in the new environment it has helped to create. I can't wait to see what it will have done by its 40th anniversary.

Bill Thompson is an independent journalist and regular commentator on the �鶹Լ�� World Service programme Digital Planet. He is currently working with the �鶹Լ�� on its archive project.