This is an upgrade edition - requiring Windows 3.0 to be installed in your system. In response to the impending release of OS/2 2.0, Microsoft developed Windows 3.1, which includes several minor improvements to Windows 3.0 (such as display of TrueType scalable fonts, developed jointly with Apple), but primarily consists of bugfixes and multimedia support. It also excludes support for Real mode, and only runs on an 80286 or better processor. Later Microsoft also released Windows 3.11, a touch-up to Windows 3.1 which includes all of the patches and updates that followed the release of Windows 3.1 in 1992. Around the same time, Microsoft released Windows for Workgroups (WfW), available both as an add-on for existing Windows 3.1 installations and in a version that included the base Windows environment and the networking extensions all in one package. Windows for Workgroups includes improved network drivers and protocol stacks, and support for peer-to-peer networking. One optional download for WfW was the "Wolverine" TCP/IP protocol stack, which allowed for easy access to the Internet through corporate networks. There are two versions of Windows for Workgroups, WfW 3.1 and WfW 3.11. Unlike the previous versions, Windows for Workgroups 3.11 only runs in 386 Enhanced mode, and requires at least an 80386SX processor.
All these versions continued version 3.0's impressive sales pace. Even though the 3.1x series still lacked most of the important features of OS/2, such as long file names, a desktop, or protection of the system against misbehaving applications, Microsoft quickly took over the OS and GUI markets for the IBM PC. The Windows API became the de-facto standard for consumer software.