Definitions for "Windows 3.1"
A 16 bit operating system and desktop interface developed by Microsoft. The first major upgrade to Windows 3.0, introduced in 1992. Windows 3.1 continues to be used, but it cannot run 32-bit applications and is only at work in legacy situations.
Windows 3.1 is the probably currently the fourth most popular variant of MS-Windows. It is lighter weight than either Windows '95 or Windows NT (but not lighter weight than GEOS) but less capable than the other two. It is made to run on top of MS-DOS and will not do much of anything if MS-DOS is not on the system. It is thus not strictly an OS per se, but nor is it a true window manager, either; rather the combination of MS-DOS and Windows 3.1 result in a full OS with GUI. Its driver support is good, but its game selection is limited. Windows 3.1 runs only on x86 based machines. It has some severe Y2K issues that may or may not be fixed.
Graphical User Interface, not an Operating System, because it relies on DOS to perform many functions. Its successor, Windows 95, is an operating system. Windows 3.1 is the minimum operating system Technet currently supports.