MS-DOS 4.0 released in June 1988 provided XMS support, support for partitions on hard disks up to 2 GB and a graphical shell. Due to large number of bugs and many programs refusing to run on it, MS-DOS 4.0 was very unpopular with the users.

Microsoft attempted to corrected many of the bugs with version 4.01, but many users simply switched back to version 3.3 and waited for a properly re-written and fully tested version - which did not come until version 5.0 in June 1991.