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Win32s is an installable add-on for Windows 3.1x, which enables 16-bit Windows to run some 32-bit executables. While it includes portions of the Win32 API, they're very minimalistic and insufficient for most 32-bit applications to run properly. For a 32-bit program to run properly under Win32s, it mustn't use more than 16MB of memory or any extended features introduced with later versions of 32-bit Windows. Some 32-bit programs, released at that time, kept backwards compatibility with Windows 3.1x by depending on them when running on 16-bit Windows. One such program was the NCSA Mosaic 2.0 web browser. Some programs included a version of Win32s in the installer, while others required the user to install the extension separately.

Also included is the famous card game Freecell, which was made to demonstrate a 32-bit app running on 16-bit Windows. The game later became a part of Windows 95.

Win32s never saw widespread usage mainly due to the following two reasons: 1) it's capabilities were very limited compared to the full Win32 API, so most of the time it was easier to make a separate 16-bit version of the program; 2) By the time of release of Windows NT and 95, 16-bit Windows was already outdated.

Known versions

The list below includes the "short" version number, the full version number with build number, the distribution formats known to exist and some additional details where available.

  • Oct. 1992 Beta (floppy and CD) - the earliest known version, has no actual version number
  • 1.0 (1.0.61 Beta - floppy and CD) - included in Win32 SDK Beta from March 1993 (build 404)
  • 1.1 (1.1.88 - Developer, MSVC32s and floppy)
  • 1.1a (1.1.89 - floppy)
  • 1.15 (1.15.103 - Developer and floppy) - also included in Windows Chicago Beta 1 SDK
  • 1.15a (1.15.111 - floppy)
  • 1.20 (1.20.123 - Developer, floppy, CD and OLE2)
  • 1.20 (1.20.127 - floppy)
  • 1.25 (1.25.139) - included in Windows 95 Beta 2 SDK
  • 1.25 (1.25.141 - floppy, CD and OLE2)
  • 1.25a (1.25.142 - floppy, CD and OLE2)
  • 1.30 (1.30.140 Beta - floppy) - included in Windows 95 Beta 2 SDK
  • 1.30 (1.30.152 Beta - floppy)
  • 1.30 (1.30.152 - floppy)
  • 1.30 (1.30.159 - floppy)
  • 1.30a (1.30.166 - Developer, floppy, CD and OLE2)
  • 1.30c (1.30.172 - Developer, floppy and CD) - the last version, released in 1996