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Q68176: Upgrading Pre-4.0 Systems with Logical Drive(s) > 32 MB

Article: Q68176
Product(s): Microsoft Disk Operating System
Version(s): MS-DOS:4.x,5.x,6.0,6.2,6.21,6.22
Operating System(s): 
Keyword(s): 
Last Modified: 17-DEC-2000

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The information in this article applies to:

- Microsoft MS-DOS operating system versions 4.0, 4.01, 5.0, 5.0a, 6.0, 6.2, 6.21, 6.22 
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SUMMARY
=======

Some original equipment manufacturers (OEMs) modified their adaptations of
MS-DOS to provide logical drives larger than 32 megabytes in versions of MS- DOS
earlier than version 4.0. This was usually implemented by using a sector size
larger than the standard value of 512 bytes. This is called "logical sectoring"
because the sector size of the drive is a logical value; that is, it is
dependent on the value in the BIOS parameter block of the drive for
bytes_per_sector. Microsoft MS-DOS versions 4.0 and later do NOT support this
logical sectoring on hard disk drives. A sector size of 512 bytes per sector is
assumed on all hard disk drives.

If you have used a version of MS-DOS that uses logical sectoring to create a
logical drive larger than 32 MB and want to upgrade to MS-DOS 4.0 or later, you
MUST either repartition the disk or use the Microsoft MS-DOS Upgrade SETUP.EXE
to convert the hard disk drive.

WARNING: 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. Returning to the previous version of MS-DOS requires either
repartitioning or using the MS-DOS Upgrade Uninstall feature.

NEC, Toshiba, Wyse, and Zenith are known to use logical sectoring, and other OEMs
may have done this as well. Compaq MS-DOS 3.31 is known to have implemented
large logical drives in the same way as Microsoft MS-DOS 4.0 and later (that is,
without logical sectoring) and therefore is version 4.0 compatible.

MORE INFORMATION
================

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- DOS Fdisk.

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" (without the quotation marks) and "5" (without the quotation marks)
  and "uninstall" (without the quotation marks)

Additional query words: 6.22 4.00 4.01 5.00 5.00a 6.00 6.20

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Keywords          :  
Technology        : kbMSDOSSearch kbMSDOS400 kbMSDOS621 kbMSDOS622 kbMSDOS620 kbMSDOS600 kbMSDOS500 kbMSDOS401 kbMSDOS500a
Version           : MS-DOS:4.x,5.x,6.0,6.2,6.21,6.22

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