Reply 20 of 47, by ynari
The question is more what software you're running on it. Technically you could potentially go down to two. I was hoping to run everything on two PCs, but for various reasons it's three.
1) Up to date system. Runs Windows 8.1 and XP. Windows 8.1 : Modern games which need a fast graphics card. XP : Games that need EAX, Windows 9x era games. Includes an X-Fi card for EAX.
2) Main retro system (almost complete). P2 400 (or something) era. Will run XP, Windows 9x (for DOS), OS/2. Features an S3 Virge (very DOS game compatible). An AWE32 (DOS music, MIDI port for Roland modules). Voodoo 2 (for very few games, to be honest)
3) Old retro system. DOS only. For DOS games which won't work on main retro system, after Sam and Max crashed and burned.
Your systems are all too fast to run particularly old DOS games. So, if you're aiming to cover most bases in one retro box my answer is 'the fastest system with an ISA slot' (so you can put in a Soundblaster, etc).
Windows compatibility is fantastic, extremely old games will still run now, with some tweaking. Therefore the only real barrier is the loss of hardware accelerated Directsound3D after XP, and a few video mode changes. At the time I loved my Voodoo2 card, but in retrospect there are very few games that require it (i.e. Tomb Raider), the others are best run in Direct3D mode.
I'm becoming vastly less precious about old computers. I've got a Cyrix MII 300 motherboard sitting around doing nothing, that I might stick on ebay. At the time I loved it, but it's too fast for particularly old DOS games, and too slow for the newest DOS games - what's the point? Then again, I don't really care about being period correct, provided the game runs exactly or better than originally envisaged.
I'd probably keep the TNT2; I suspect it's got better DOS compatibility than later cards. However, I do have a TNT somewhere, and it doesn't support the ability to move the screen up and down used in Ultima VII, where the screen shakes in the presence of cyclops.