DJL Software (for "Dave and John Looker Software") is mainly known as the co-author of the Speedlock protection system.
A fast loader and protection used on many cassette games, and as a protection on disc games.
DJL was also the author of several Amstrad games including 3d Stunt Rider and Nigel Mansell's Grand Prix, in addition to self-published titles such as [Frogger].