Oh please ...
I've been in micro-computing since the late 70's and there were lots of options that didn't involve Microsoft, IBM or any of the other monopolies.
The real kudos need to go to Gary Kildall of Digital Research that created CP/M which was the basis of MS-DOS as Bill Gates purchased a 16-bit clone of CP/M to resell to IBM. If it wasn't for CP/M there wouldn't have been anything to clone and MS wouldn't have had anything to resell to IBM and history would be very different.
For those what wish to dispute this point, go look in your PSP, the PSP is the program segment prefix that prefixes the code segment of every windows app and the bytes at 0005 redirect to INT 21.
Why is this important?
Because the call to the CP/M operating system and later MS-DOS was CALL 0005 with all the parameters to the OS and it was still a part of Windows as late as Windows 98 last time I checked. MS-DOS changed that call to INT 21 but maintained the vector at 0005 for backwards compatibility with CP/M software ported to early versions of MS-DOS.
I haven't looked lately, but Vista is probably still CP/M compatible :)