Possible Data Loss with LBA and INT13 Extensions

Last reviewed: December 15, 1997
Article ID: Q148821

95 WINDOWS kbhw

The information in this article applies to:

Microsoft Windows 95

SYMPTOMS

After you perform one of the following actions, the contents of some Enhanced IDE (EIDE) hard disks may not seem to be correct:

Choosing "Restart the computer in MS-DOS mode" from the Shut Down menu.
Starting an MS-DOS-based program that is configured to run in MS-DOS mode.

Specifically, if there are multiple partitions on a large EIDE hard disk, the extended partitions (usually drive letters D and higher) seem to contain the contents of the primary partition (usually drive C), or to be corrupted.

WARNING: In this situation, attempts to use disk-repair utilities such as ScanDisk to repair the apparent corruption will cause data corruption on the primary partition of the affected drive.

Any action that attempts to write data to the extended partitions when this symptom is observed may also result in data corruption.

Running the CHKDSK command when this symptom is observed may result in a "Probable non-DOS disk" message.

CAUSE

This situation is known to occur only when all of the following conditions exist:

The hard disk is a large (>504 MB) Enhanced IDE hard disk.
The hard disk is accessed using Logical Block Addressing (LBA).
The hard disk has been partitioned into multiple partitions with the Windows 95 version of FDISK, or another partitioning utility that creates MS-DOS extended partition types 0x0E and 0x0F.
The system BIOS supports INT13 extensions to access hard disk devices.
You have exited to MS-DOS mode from Windows 95 without rebooting the computer.

Under these circumstances, certain data structures maintained by the operating system for accessing these logical drives become corrupted in the transition from protected mode to real mode.

This does not occur when you boot the computer to a command prompt or from a floppy disk.

RESOLUTION

This issue is resolved by the following updated file for Windows 95:

   DISKTSD.VXD version 4.00.952 (dated 3/22/96) and later

Installation

To install the updated file, use the following steps:

Download the Dsktsupd.exe file from one of the online services listed below to an empty folder.
In My Computer or Windows Explorer, double-click the Dsktsupd.exe file you downloaded in step 1.
Follow the instructions on the screen.
After the installation process is finished, shut down and then restart your computer.

Instructions for Downloading

You can find DSKTSUPD.EXE (size: 150624 bytes) 
                         , a self-extracting file, on the following

services:

Microsoft's World Wide Web Site on the Internet

      On the www.microsoft.com home page, click the Support icon.
      Click Knowledge Base, and select the product.
      Enter kbfile DSKTSUPD.EXE (size: 150624 bytes) 
                               , and click GO!
      Open the article, and click the button to download the file.

Internet (anonymous FTP)

      ftp ftp.microsoft.com
      Change to the Softlib/Mslfiles folder.
      Get DSKTSUPD.EXE (size: 150624 bytes)

Microsoft Download Service (MSDL)

      Dial (425) 936-6735 to connect to MSDL
      Download DSKTSUPD.EXE (size: 150624 bytes)

For additional information about downloading, please see the following article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q119591
   TITLE     : How to Obtain Microsoft Support Files from Online Services

MORE INFORMATION

For additional information about INT13H extensions, please see the following article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q122052
   TITLE     : Logical Block Addressing (LBA) Defined

For additional information about the use of large hard disks with MS-DOS and Windows 95, please see the following article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q126855
   TITLE     : Windows 95 Support for Large IDE Hard Disks

Workaround

To work around this issue, in the event you do not have the updated DSKTSUPD.EXE file, use either of the following methods:

Method 1

Avoid exiting to MS-DOS mode from within Windows 95. To run programs that require MS-DOS mode, boot to a command prompt instead of Windows.

Method 2

Repartition the hard disk using one of the following methods.

WARNING: Repartitioning the hard disk will delete all data in the current partitions (logical disks). Make sure to back up your data before repartitioning the hard disk.

Repartition the hard disk into a single primary partition.
Repartition the hard disk by starting FDISK with the following command line:
```
      FDISK /X
```
This disables support for the LBA extended partition types 0x0E and 0x0F, and uses the older partition types 0x05 and 0x06 instead.
Repartition the hard disk with an older version of FDISK (prior to Windows 95) that does not support the LBA extended partition types.
Repartition the hard disk using a third-party tool that does not use the LBA extended partition types.

KBCategory: kbhw
KBSubcategory: win95 winboot diskmem
Additional reference words: 95 XINT13 INT13h INT
Keywords : diskmem win95 winboot kbhw
Version : 95
Platform : WINDOWS

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Last reviewed: December 15, 1997
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