It’s not so much Microsoft’s drivers as VGA. The trouble with VGA is that it’s almost, but not quite, unaccelerated. The general lack of acceleration means that the guest CPU has to do quite a few memory accesses to shuffle pixels around. But the “acceleration” means that the VGA memory does not behave like typical memory at all, and both reads and writes have side effects. That means all VGA memory accesses generally have to be trapped, and the overhead of that is significant, especially with older VT-x systems.

The irony of entirely unaccelerated VESA software (where the graphics card is treated like a dumb framebuffer) is that it’s actually ridiculously fast in a VM. The graphics memory works just like regular RAM and the guest can access it without having to go through a slow bus. It can easily run much faster than on a physical system.

You can try something like OS/2 1.3 in VirtualBox both with and without VT-x. You’ll likely find that the VGA performance with VT-x is noticeably slower, even though most other operations are faster.

The commonality of Microsoft and dragging windows seems to be quite painful….. But I recall it kind of dogging on hardware as well back then. Of course I may have thought my ‘awesome’ 16Mhz machine with my memory and all peripherals on the glorious ISA bus….