Adobe ported these products to the Microsoft Windows operating system platform, where they managed font display by patching into Windows (3.0, 3.1x, 95, 98, Me) at a very low level. The design of Windows NT made this kind of patching unviable, and Microsoft initially responded by allowing Type 1 fonts to be converted to TrueType on install, but in Windows NT 4.0, Microsoft added "font driver" support to allow ATM to provide Type 1 support (and in theory other font drivers for other types).