ARM
ARM, Acorn RISC Machine, is a 32-bit CPU originally designed by Sophie Wilson and Steve Furber of Acorn Computers of Cambridge, England. The acronym has since been changed to mean "Advanced RISC Machines" after the original Acorn Computers company was no more.
Acorn Computers used the 6502 8-bit CPU, e.g. in their BBC Micro, which started to get a bit aged around 1983. Wilson and Furber concluded after some testing that the Nat Semi 32016 and the Motorola 68000, and other CPUs they tested were not very efficient in using the memory bandwidth that had become available at the time (they all performed at around 4Mbit/s). To avoid that CPU bottleneck Acorn wanted something better and started looking into CPU design. At first Wilson and Furber visited some traditional microprosessor plants and found large buildings with thousands of engineers. But, because Wilson was a huge fan of the 6502 processor (and has been called "the best 6502 programmer ever" by Personal Computer World's Guy Kewney), they visited Western Design Center where Bill Mensch (designer of the CMOS version of the 6502, the 65C02) was busy designing their next generation CPU. Seeing the very small scale of the operation Wilson and Furber thought "we could do that", went home, and designed what would be the 32-bit ARM CPU, now referred to as ARM1. It used 25000 transistors. The first samples were ready in April 1985.
ARM is most known for its low power consumption, and is the main reason the architecture became so popular with mobile devices where it has about 95% of the market. The designers were not trying to create a CPU with particularly low power consumption, that was not much of a concern back in 1983. When the first sample was plugged into a development board the CPU worked perfectly (quite an achievement for a first version), but Wilson noticed that the meter in series with the power line to the CPU showed zero, so something was wrong. It turned out that the development board had a fault, it did not provide power to the CPU itself, only to the logic chips around it. The CPU was running only on leakage from the logic circuits. In the end it turned out that the CPU only needed one tenth of a watt, but this was all accidental to the design even though it was what secured ARMs huge market today, with several billions of CPUs sold every year (in comparision Intel has been selling around 1 billion CPUs per year lately).
Today the ARM design is held by ARM Holdings (often called just ARM). The company is still located in Cambridge, UK. The architecture now comes in a lot of incarnations, including 64-bit versions.
