IIRC, Win32 is regarded as the name for the Windows API, and Win32NT is the name of the API/platform for all Windows versions derived from Windows NT. And Windows 95 is not Win32NT, because the NT and 9x API's were closely related and mostly compatible, but not the same. Also, the Win32NT API is the same on both x86 and x64 (and Itanium, which is a very different beast from x64).