Well XP is still there in some way in win 7 but its a virtual machine addon (XP mode)

i use it mostly for older compilers like msvc 6 and dos games. Sadly 3D accceleration is a nogo with XP mode
so gaming in XP mode is a bit meh

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Btw XP was released 25. oktober 2001 so allmost 13 years

but lets not split hairs about that.
And i agree that support for older games would be nice, sadly i doubt microsoft will invest the time supporting that.
Win 8 is in my eyes a disaster allthough i like its speed i hate being forced into metro whenever i try to open something, i could live with it if microsoft let me have the option of selecting what
interface i want when installing that would probably save it for them also.
Besides that im actually impressed with how well it runs on older machines

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Besides that i fully support having multiple OS like XP / 98 / Win 7 just keep in mind that the older ones might have flaws so be sure to have adequate protection if you insist on using them online.
Biggest problem with say 98 is that no modern security solution will run on it :S so its rather exposed.
Productivity is a state of mind.