A landmark insofar as it was the first ARM-based computer. Planned as a successor to the Acorn BBC series of educational machines, it was a bit of a dead end in personal computing terms -- a British also-ran to the Amiga and Atari ST families -- but the descendants of its CPU are now the only personal computing architecture out there to still be competing with Intel (aaaand if you classify tablets as personal computers, they're trouncing the x86 family on volume).