To test whether the new version of MS-DOS correctly accesses the disk, boot
the new version and run CHKDSK (not CHKDSK /F). You should get the same
output as the current MS-DOS.
Repartitioning deletes all information stored on the disk. It may be
necessary to delete the current partitions with the current version of MS-
DOS Fdisk. The new partitions MUST be created with the new version of MS-
The Microsoft MS-DOS Upgrade SETUP.EXE converts all MS-DOS compatible
partitions with logical sectors into standard 512-byte sectors. After you
upgrade the hard disk drive, booting the previous version of MS-DOS and
writing information to the hard disk drive may result in data corruption.
The SETUP.EXE file that ships in Microsoft MS-DOS versions 5.0 and later
(generic OEM or packaged product) does not convert partitions with logical
sectoring into standard 512-byte sectors. Repartitioning can only be
avoided by using the Microsoft MS-DOS Upgrade SETUP.EXE.
To return to the previous version of MS-DOS after upgrading using Microsoft
MS-DOS Upgrade SETUP.EXE, the best option is to use the Uninstall program.
UNINSTAL.EXE replaces the previous MS-DOS version and converts the large
partitions to their previous states. To use UNINSTAL.EXE to return to the
previous MS-DOS version, boot from the Uninstall #1 disk created while
upgrading to MS-DOS 5.0 or later.
NOTE: If DELOLDOS has been run, Uninstall cannot return the drive to its
pre-upgrade state. Returning to the previous version of MS-DOS requires
repartitioning, which destroys all information stored on the drive.
For more information on Uninstall, query on the following words here in the
Microsoft Knowledge Base:
ms-dos and 5 and uninstall