Some Windows 3.1 apps were simply "too evil" for Windows 95 to support, says Microsoft veteran

Windows 95 developers tried to keep older software running.

Microsoft built custom compatibility fixes in the 1990s.

Raymond Chen said some Windows 3.1 programs and drivers were completely incompatible.

Some programs misused memory handles, and Windows 95 used a different memory model with a 32-bit heap instead of Windows 3.1's 16-bit heap.

Other software broke on version checks, and Windows 95 had to support MS-DOS, 16-bit Windows, and 32-bit Win32 software.