3. MS-DOS has a kernel which is an executable loaded into memory first and a shell, e.g. command.com. Windows 3.1 carried everything out via assorted software interrupts and BIOS calls, except for video access, which was done by the driver and probably primarily involved direct video access. By "pass commands to MS-DOS" it means use interrupt 21h, MS-DOS services. The heavy use of the DOS interrupt and BIOS calls meant that windows could support anything dos could support. If you had a special keyboard which operated via a TSR, which in turn was typically activated by INT 16h (keyboard bios functions) as it had patched the vector table, it would work in windows, too.

Thanks to "Assembly Language for Intel-Based Computers" by Kip R. Irvine (ISBN 0-13-091013-9) for keeping me factual...