The Common Lisp function
software-type returns a generic name for the Operating System. The Common Lisp function
software-version returns information about the version of the Operating System.
In particular software-type can be used to distinguish between systems based on Windows 95 and those based on Windows NT. software-version allows you to identify variants such as Windows Millennium Edition, Windows 2000, Windows XP, Windows Vista and so on. See the manual pages for details.