This elegant ISA design (minimalist because of cost constraints) powered many iconic computer systems, which went on to change the world: eg the Apple II because… well Apple, and the BBC micro. Acorn’s BBC micro was designed for expandability; of ‘built-in’ languages (Lisp, Pascal, BCPL) alongside the BASIC system (whose design by Sophie Wilson was a model of ingenuity). It also became a key design tool in the development of the ARM processor. Which you may have heard of.