Speedlock was a software protection system used on the ZX Spectrum and the Amstrad CPC, written by David Aubrey-Jones and David Looker in 1983. The two programmers had become frustrated at the slow loading times of the computer's tape loading system, and realised it would be possible to write a better one. The prototype sat unused for about a year, but was finally picked up by Ocean Software on Daley Thompson's Decathlon, released in late 1984. It was subsequently used by U.S. Gold and for several titles by Ultimate Play the Game, amongst others. Speedlock was also ported to the Amstrad CPC in 1985.