I really can't say which variations are actually out there but you have `cygwin` twice.

However, I thought about a potentially more reliable method. Every windows I know of has an environment variable `WINDIR` which denotes the Windows installation directory. So `!!ENV['WINDIR']` should do the trick regardless of used compiler and Windows version. [List of Environment Variables in Windows XP, Vista and 7](http://www.askvg.com/list-of-environment-variables-in-windows-xp-vista-and-7/). Can't confirm for Windows 8 but I'm pretty sure that it's still there since a lot of stuff depends on this AFAIK.