svfn: that's a nice collection you have there. i am still halfway from building my P2. playing on real hardware would be preferable if these things were not so hard (or expensive) to find now, especially the old motherboards, 3dfx chips, Aureal sound cards or sound canvas/MT-32 etc.
eventually GOG/Steam gave up support for older OS and that includes XP. it is inevitable really =/
personally, i don't miss XP that much and since it's still possible to dual boot using most modern hardware. but for older OS like MS-DOS/Win95/98.. well i guess DOS box is convenient for some games.
Yeah. I TRY to make everything work (as intended) on "modern" hardware and software, but in some cases, it just won't work.
The list is not HUGE. DOSBox (another thing that Microsoft claimed was "impossible" to include in Window) works marvelously, as does ScummVM, and both are used extensively by GoG in making "old games" work on current systems, of course.
But there are plenty of things which won't run on current systems. The "Jane's Combat Sims" games are a HUGE one, frankly... if EA ever decided to try to re-release those (updated for modern systems) the need for older hardware would drop precipitously, no doubt. All the old Star Trek reference works... none will run on modern systems (due to being so heavily built upon Apple's Quicktime 2.x and 3.x, mainly... but they can run in a VM.
But... just for one example where nothing but real hardware will work... "Jetfighter III." I originally ran it on a system with a Voodoo Banshee (later replacing that with an early Geforce nVidia card and an add-on Voodoo2, providing real direct3D, OpenGL, and GLide) and using a Creative Sound Blaster AWE64 (with memory expansion chip installed).
Honestly, the AWE64 still outperforms any system I've ever seen for realistic digital sound generation in a PC. The AWE64 was the pinnacle of "Midi which sounds like real instrumental music" on the PC, but pre-recorded "redbook audio" came onto the scene around then and MIDI died off almost entirely (and people today think "Midi is tinny, fake-sounding garbage," when in fact, it was able to create truly realistic music... all digitally, without being "recorded" per-se).
Jetfighter III was about as much fun as I've ever had in a flight sim... on the original system. But it's essentially unplayable on anything since then. So, my Win98SE machine has the AWE64 and and Voodoo2 installed, and running, to this day.
My wife calls me a "hoarder" because she thinks I should have thrown away these "old, obsolete computers." But... they still have value, and not just from a "hoarder" standpoint. :)