Why did Windows 95 setup use three operating systems?

I never thought of Windows 3.1 as an OS. The other 2 was MS-DOS and Windows 95.

Agree, the terminology in those days was “shell”.

Though Windows 95 was arguably similar running atop “DOS 7” it actually imposes its own 32-bit environment with its own “protected mode” drivers once booted. Dropping to DOS reverted to “real mode”.

So did the lastest Win3.1 for workgroups, just MS spared all the fanfare for Win95. Not sure if the 3.1 version in the installers does.

Windows 3.1 was just a graphical shell. All the drivers and stuff were still managed by DOS. You still needed to configure your system with config.sys

EDIT it’s coming back to me. Windows 3.1 did have a a subsystem for running 32 bit apps called Win32 I think that’s what you mean. This was very much in the application space though.

It still used cooperative multitasking and Win 95 introduced preemptive.

It was Win32s https://en.m.wikipedia.org/wiki/Win32s

Thanks

”Win32s lacked a number of Windows NT functions, including multi-threading, asynchronous I/O, newer serial port functions and many GDI extensions. This generally limited it to "Win32s applications" which were specifically designed for the Win32s platform,[4] although some standard Win32 programs would work correctly”

It was a strange time back then for anyone who wanted to get online. Win3.1 had no TCP/IP stack so many folks used a third party download called Trumpet Winsock. IIRC you might have needed win32s in order to use it.

Looking back, Microsoft were clearly in an incredibly complicated transitioning phase, with very little margin for error (no patching over the Internet!)