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Many have been greatly annoyed at the lack of compatibility across the different versions of Windows. With newer editions of the operating system, older applications break or simply do not run at all on later versions of Windows at all.
This continues to be a problem Microsoft is trying to solve. With Windows 7 came 'Windows XP Mode' to allow applications to run as if they were running on Windows XP without having to 'Bootcamp' in and out of different operating systems. Windows 8 is expected to have a 'Windows 7 Mode' which may indicate further broken backwards compatibility.