Comment by philipstorry

Windows 1-3 ran on top of DOS, with a small caveat for Windows 3.x

Windows 3.x running in 386 Enhanced Mode had a very small multi-threaded preemptive kernel, which it used to handle its MS-DOS windows. So whilst each Windows program ran cooperatively within Windows and had no memory protection, Windows itself and each DOS window it opened were pre-emptively multitasked and had better memory protection. This wasn't very well documented, but it's the beginnings of Windows no longer running on top of DOS and instead taking over control of the machine.

Windows 3.1 also introduced "32 Bit Disk Access" which used a custom disk driver to bypass DOS and the BIOS and speed things up. Windows 3.11 (Windows for Workgroups) extended that to "32 Bit File Access", which bypassed DOS for file operations.

Windows 95 only used DOS as a bootstrapper. It would be completely incorrect to say that Windows 95 "ran on top of DOS", as once Windows 95 finished booting it had effectively pulled the rug out from DOS and was handling all I/O, memory operations, and so forth. It would be like saying that Linux runs on top of GRUB - GRUB is no longer in control of the machine, so it's just not true.

Not that I'm saying you were stating Windows 95 ran on top of DOS, you understand! I'm just putting this information here for educational reasons and expanding on your comment. ;-)