I just wanted to add that Windows 3.X is capable of running independently of DOS and BIOS calls. By default yes, it uses the BIOS for disk access. But with a disk driver (e.g. Microhouse driver, FastDisk driver), Windows 3.X can live entirely in 32-bit protected mode. Windows 95/98/Me are the same way, they are real 16/32-bit hybrid kernels that used DOS as a bootstrap but nothing more.