pypa/virtualenv — pull request #582 by schlamar (2014-03-21 13:05:10+00:00)
Title: Query 32bit and 64bit Python versions on Windows.

On a 64bit Windows, 32bit applications does not query for 64bit application's registry entries and vice versa. But with the appropriate flags you can switch the queried view. More details are in this MSDN article: http://msdn.microsoft.com/en-us/library/aa384129(v=VS.85).aspx