I worked on an IT helpdesk at an insurance company for the summer in 1996. I had to support IBM PS/2 PCs that would tri-boot Windows 3.1, OS/2 Warp, and Dos. No one operating system had all of what they needed.
Funny side story:
They had a token ring network, and in the network room, there weren't enough physical network ports for all of the employees. Every morning someone would call the helpdesk to say their computer was couldn't access the network, I'd look at the N network cables, find one that without lights to indicate that cable was in use, unplug the inactive one, and plug in the cable of the person w/o access. It turned out on most days enough people called in sick or were on vacation that we could get everyone who needed a connection wired up :)
Anything that decided to hit the hardware directly from DOS, or did something that OS/2 didn't support in windows just crashed or had undefined behaviour.
Even windows in protected mode couldn't do all DOS things any more. Even if you dropped out of protected mode, and fiddled around too much you'd end up breaking windows when you switched back to it.
Back then you'd have all manner of weird DRM schemes which used dongles on the parallel port, not to mention manually set IRQs, I/O Ports and blocks of high mem (between 640K and 1M) where your device drivers were baked into the DOS application, NOT the operating system. There were some driver.sys type drivers for random hardware, but mostly it was just cheaper to write the driver inside the app itself.
Programming under DOS was more akin to writing to an Arduino rather than linux/windows back then.
Funny side story:
They had a token ring network, and in the network room, there weren't enough physical network ports for all of the employees. Every morning someone would call the helpdesk to say their computer was couldn't access the network, I'd look at the N network cables, find one that without lights to indicate that cable was in use, unplug the inactive one, and plug in the cable of the person w/o access. It turned out on most days enough people called in sick or were on vacation that we could get everyone who needed a connection wired up :)