Removing Non-DOS Partitions with Debug
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The information in this article applies to:
Microsoft MS-DOS operating system versions 6.0, 6.2, 6.21
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SUMMARY
Introduction
There are currently several different versions of MS-DOS in the
personal-computer environment, both in the OEM-licensed versions and in the
Microsoft packaged-product versions. The hard-disk-management capabilities
of MS-DOS vary from one version to another. For example, MS-DOS versions 3.2
and 3.21 can address a single hard-disk partition of up to 32 megabytes
(MB); MS-DOS version 3.3 can address multiple hard-disk partitions, with a
primary DOS partition of up to 32 MB and an extended DOS partition
containing logical drives of up to 32 MB each; and MS-DOS versions 4.0,
4.01, 5.0, 6.0, and 6.2 can address multiple hard-disk partitions with sizes
up to 2 gigabytes (GB).
For those using versions of MS-DOS that have lesser levels of hard- disk
support, such as MS-DOS versions 3.2 and 3.21, there are a number of
third-party hard-disk-management software packages that allow MS- DOS to
access multiple partitions and/or partitions in excess of 32 MB. However,
these third-party packages may use non-DOS constructs to assist in managing
the hard disk, possibly including non-DOS partitions. These non-DOS
constructs can cause problems when you upgrade to later versions of MS-DOS
because versions of MS-DOS earlier than 5.0 assume that non-DOS constructs
are owned by another operating system and, therefore, do not use, delete, or
change non-DOS partitions or other non-DOS constructs in any way.
WARNING: Some computers require the use of third-party hard-disk-
partitioning software because the system ROM BIOS does not fully support the
drive parameters of the hard disk that is being used or because the hard
disk has more than 1024 data cylinders. If you are unsure if your system
supports your hard disk, consult your hardware manufacturer or the
manufacturer of your partitioning software before proceeding.
To detect if your system makes use of Drive Overlay software, see the
following article:
Q186057 How to Tell If Drive Overlay Program Is Installed in Windows
Using Debug to Remove a Non-DOS Partition
The Debug script on the following page, used with the MS-DOS Debug program,
deletes non-DOS partitions when you upgrade to a new version of MS-DOS,
enabling the entire hard disk to be used by MS-DOS. It does so, however, by
clearing out the entire partition table on the hard disk, which results in
the deletion of ALL partitions on the hard disk. You need to use this method
if your current version of MS-DOS cannot delete non-DOS partitions.
WARNING: Because all data on your hard disk will be destroyed by this
procedure, you must back up your hard disk before using this Debug script.
There are two ways to use the following Debug script:
Run Debug and type the Debug commands from the center column of Table 1 at
the corresponding Debug prompt. (The left column of the table shows the
prompts that are displayed by Debug. You do not need to type the comments in
the right column.)
-or-
Type the command in the center column of Table 1 into a file using a text
editor such as MS-DOS Editor and then use input redirection to feed the
resulting file into Debug. For example, if you typed the commands into a
file called HDPART.SCR, you would clear your partition table by typing the
following at the MS-DOS command prompt and then pressing ENTER:
debug < hdpart.scr
Table 1: Debug Script to Erase Hard-Disk Partition Table
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Debug Enter Debug Comments
Prompts Commands
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- A 100 Assemble from CS:0100.
nnnn:0100 INT 13 Call interrupt 13.
nnnn:0102 press the (nnnn in the segment address).
ENTER key
- RAX Replace AX register.
AX 0000
: 0301 Write on sector.
- RBX Replace BX register.
BX 0000
: 0200 Start from ES:200.
- F 200 L 200 0 We want to write zeros.
- RCX Replace CX register.
CX 0000
: 0001 Cylinder, 0, sector 1.
- RDX Replace DX register.
DX 0000
: 0080 First physical hard disk, head
0. (Substitute 0081 for this
entry if you are clearing the
table on the second physical
hard disk, 0082 if you are
clearing the third physical
hard disk, and so forth).
- P Proceed (Debug will display
several lines of information).
- Q Quit Debug.
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This script completely clears the partition table on your hard disk,
preparing the hard disk for repartitioning using the MS-DOS Fdisk program.
(When you run Fdisk for the first time after using this procedure and before
reinstalling MS-DOS, the message "No partitions defined" should be displayed
if the partition deletion procedure was successful.) For more information
about using Fdisk, see the Microsoft MS-DOS" User's Guide and Reference" for
version 3.2, 3.21, 3.3, 4.0, 4.01, or 5.0, or the Microsoft MS-DOS" User's
Guide" for version 6.0 or 6.2.
For additional information on how to recreate a partition using the Fdisk
utility, click the article number below to view the article in the Microsoft
Knowledge Base:
Q255867 How to Use Fdisk and Format to Partition or Repartition a Hard Disk
Non-DOS partitions on your hard disk are also erased if you perform a
low-level format. Consult your hardware manufacturer for specific
instructions on performing a low-level format on your hard disk.
WARNING: Performing a low-level format will completely erase all data on
your hard disk, including all defined partitions.
