That was 12th August 1981. I first set hands on one in April 1987. Amstrad created the first home-priced PC-compatible in 1986. Still, what the IBM PC did to the computer world was clear to any home computer enthusiast of the day since 1983 at the very least.
What did the IBM PC do? Just remember the PCs before the PC. Apple, of course, and Commodore and Sinclair, but also Acorn, BBC Micro, Olivetti, Atari, Texas Instruments, others I will remember when I read their names – they have yet to appear on
What about them? Less powerful? Less sophisticated?  Come on! IBM’s came with optional floppy disk drive and standard *cassette recorder* (the second round 9-pin plug next to the keyboards’ on the back, who can remember that?). Base RAM was 16 kB, maximum 256. Color and graphics optional.
The real difference was that IBM’s brand gave their PC clearance to enter business environments. That, and the choice of an open architecture 3rd parties could thrive on and push, made the day. All other personal computers had been tied to closed business model that prevented any of them to prevail on the others and kept market for all of them comparatively marginal.
A good assessment and outlook of the IBM PC’s history is on The Economist:
A richer summary nicely tying it all to Ray Ozzie’s latest announcements is on BBC: