Multitasking MS-DOS 4.00 4.00

Release notes

This is the multitasking version of MS-DOS that Microsoft originally planned to release as MS-DOS 4. It was a parallel project to DOS, never released to the regular consumer market, and Microsoft backtracked to base its next consumer release off of DOS 3.3.

Note that although it calls itself "MS-DOS Version 4.00", it is a different product than the MS-DOS 4 that actually shipped.