but the OPs question didnt say gaming systems, he said systems ?
so surely this would include computer systems, especialy since the principle product of these systems were games, the likes of amiga's although caperble were games machines principly.
if you take the example that out of what, 100,000 software titles for an amiga 99% of them would be games, wheras the 60 or so available for the odyssey2 (no doubt classed a gaming system), 2 programming, 6-7 educational making it only 85% a gaming system...far less than the amiga, Ti99, etc.
taking the other extreem, are todays consoles games machine or multi-media devices, most play films, music, internet communications, gaming is just one facet of thier use the same as computers of thier day.
An XBOX is principaly a games PC.
(all the above figures were 99% inacurate)..but a realistic guess.
I agree with the variations on principly the same unit though
eg..megadrive 1 & 2, playstaion, psone etc.
you have to allow for specific games backward compatiblity though, like playing playstationstandard games on a playstation 2
you couldnt rule out a playstationif you had an PS2 as well, since it cant play PS2 games.