You're thinking of what is sometimes called "European MS-DOS 4.0" which did indeed have limited multitasking features, including shared memory and pipes: https

You're thinking of what is sometimes called "European MS-DOS 4.0" which did indeed have limited multitasking features, including shared memory and pipes: https://en.wikipedia.org/wiki/MS-DOS_4.0_(multitasking) https://en.wikipedia.org/wiki/MS-DOS_4.0_(multitasking) https://virtuallyfun.com/2013/03/17/european-ms-dos-4-00-aka-multitasking-dos/ https://virtuallyfun.com/2013/03/17/european-ms-dos-4-00-aka... It should not be confused with the mostly unrelated DOS 4.0 later released. A Microsoft executive later said the multitasking DOS should probably not have been named "4.0" because it created a lot of confusion.