You don't even have to go back as far as the old 8 and 16 bit platforms -- even many games written during the past decade are completely unusable since they were written under Windows 95/98/ME and aren't compatible with XP/Vista... Even in compatibility mode you can't run them.
(Although I've played a few through a virtual Win98 in VMWare under XP -- that works OK, but it's hardly mainstream. At least old games aren't that CPU intensive on current computers, so you can deal with the virtualization overhead)
(Although I've played a few through a virtual Win98 in VMWare under XP -- that works OK, but it's hardly mainstream. At least old games aren't that CPU intensive on current computers, so you can deal with the virtualization overhead)