A kick-ass mid-range computer invented by IBM. Long family tree going back to System/3 (and probably before). Updated through the years at hardware and software levels and today forms a very fine platform on which to build quality enterprise systems. Oh yeah, and don't forget RPG (Report Program Generator) one of the dogs of the programming language world that seems to follow AS/400 round.
IBM have now started calling them iSeries eServers or some old bollocks like that. Whatever. To droves of ageing programmers (who still think the RPG Debugging Template, flowchart stencils, Dire Straits, Jethro Tull, real ale, war gaming and cricket) are all 'cool', they represent a rock to cling to.
"I love AS/400's - they're the best goddam box to poke around in - even beats the milf's I pick up at bars after a long day spec'ing RPG programs." Hiram J. Corksacker III, Software Engineer, Portland, OR.