Multitasking MS-DOS 4.00 (1985) 8 DOS

Multitasking "MS-DOS 4.00" is a developmental version of MS-DOS that was never released to retail consumers. It was eventually licensed to some companies for internal use. Development started in parallel during the DOS 2.x days, and was intended to be the successor to MS-DOS 3.x. It would have competed against Digital Research's Concurrent DOS.

• 4.00