The ARM microprocessor dominates the world of mobile and embedded computing, and over 200 billion ARM-powered microchips have been manufactured to date. The origins of the ARM can be traced back to a small UK supplier of desk-top machines, Acorn Computers Ltd, in the early 1980s, for whose staff the original ARM (then the ‘Acorn RISC Machine’) was a first attempt at designing a microprocessor. A lot has changed over the subsequent 40 years, and today the ARM is used in almost all mobile phones, the world’s fastest supercomputer, and many other computing systems including the SpiNNaker brain-modelling computer at the University of Manchester.