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Troubleshooting MS-DOS Compatibility Mode on Hard Disks

This article was previously published under Q130179
The Performance tab in System properties shows that one or more of thehard disks in your computer is using MS-DOS Compatibility mode. MS-DOScompatibility mode may be in use either for the file system or forvirtual memory. You may receive the following message:
Compatibility Mode Paging reduces overall system performance
MS-DOS Compatibility mode may be in use for any of the following reasons:
  • An "unsafe" device driver, memory-resident program, or virus hooked the INT21h or INT13h chain before Windows is loaded.
  • The hard disk controller in your computer was not detected by Windows.
  • The hard disk controller was removed from the current configuration in Device Manager.
  • There is a resource conflict between the hard disk controller and another hardware device.
  • The Windows protected-mode driver is missing or damaged.
  • The Windows 32-bit protected-mode disk drivers detected an unsupportable configuration or incompatible hardware.
  • You are running Windows Millennium Edition (Me) and have used Drive Copy 2.0 by Powerquest to copy the contents of one hard disk to another hard disk.
To correct the behavior, follow these steps:
  1. If you used Drive Image 2.0 by Powerquest, contact Powerquest for a version of the software that is compatible with Windows Me.
  2. Use the Performance tab in System properties to identify which drive is using MS-DOS Compatibility mode and why.

    NOTE: Floppy disk drives and CD-ROM drives operating in MS-DOS Compatibility mode cause the Performance tab to display the message "Some drives are using MS-DOS compatibility" for the file system, but this article applies only to troubleshooting hard disks operating in MS-DOS Compatibility mode.

    For additional information about troubleshooting floppy disk drives, click the article number below to view the article in the Microsoft Knowledge Base:
    131690 Troubleshooting Floppy Disk Drive Problems in Windows
    1. If the driver name listed as causing MS-DOS Compatibility mode is Mbrint13.sys, your computer may be infected with a boot-sector virus, or you are running real-mode geometry translation software (for an IDE hard disk with more than 1024 cylinders) that is not compatible with Windows protected-mode disk drivers.

      For additional information about real-mode geometry translation software that is compatible with Windows protected-mode disk drivers, click the article number below to view the article in the Microsoft Knowledge Base:
      126855 Windows Support for Large IDE Hard Disks
      Disk Manager 6.03 is supported in protected mode on hard disks on the primary IDE channel and when DriveSpace disk compression is not installed. For drives on the secondary IDE channel, Disk Manager 7.0 or later is required. When using the DriveSpace compression software that is included with Microsoft Windows and Microsoft Plus!, Disk Manager 7.04 or later must be used.
      For additional information, click the article number below to view the article in the Microsoft Knowledge Base:
      126855 Windows Support for Large IDE Hard Disks
      For additional information about detecting and removing boot-sector viruses, click the article number below to view the article in the Microsoft Knowledge Base:
      82923 Methods to Detect a Boot-Sector Virus
      129972 Description of Computer Viruses
      49500 List of Antivirus Software Vendors
    2. If a driver that is listed in the Config.sys file is named, contact the driver's manufacturer to determine whether there is a version of the driver that enables protected-mode access in Windows.

      If no driver is listed on the Performance tab, continue with Step 3.
  3. Check to make sure that the hard disk controller is listed in Device Manager. If it is not listed, install it with the Add New Hardware Wizard. If the Wizard does not detect the controller, run the Wizard again but do not let the Wizard detect the hardware in your computer. Instead, select the controller from the hardware list. If the controller is not listed, contact the manufacturer of the hard disk controller to determine whether there is a Windows protected-mode disk driver or a Windows 3.1 32-bit disk access (FastDisk) driver available.

    NOTE: If the hard disk controller is listed in Device Manager but has a red X over it, it has been removed from the current hardware profile. Click Properties for the controller in Device Manager, and then click the check box that corresponds to the current hardware profile under Device Usage.
  4. If the hard disk controller is listed in Device Manager but has a yellow exclamation point over it, there is an IRQ, I/O, DMA, or RAM address conflict with another device, the protected-mode driver is absent or damaged, or the "Disable all 32-bit protected-mode disk drivers" check box is selected in File System properties.

    1. Check to make sure that the "Disable all 32-bit protected-mode disk drivers" check box has not been selected on the Troubleshooting tab in File System properties. To access this tab, double-click System in Control Panel, click the Performance tab, and then click File System.
    2. Resolve any resource (IRQ, I/O, DMA, or RAM address) conflicts with other devices. Consult the controller's documentation for information about resource usage and changing resource usage.
    3. Check to make sure that the protected-mode driver is in the Windows\SYSTEM\IOSUBSYS directory and is loading properly. To determine which driver is providing 32-bit disk access, click Properties for the controller in Device Manager and click the Driver tab to see which driver files are associated with the controller.

      NOTE: If you are using an IDE, EIDE, or ESDI hard disk controller, the Driver tab may not be present when you click Properties for the controller in Device Manager. Unless you are using a third-party driver, Esdi_506.pdr is the protected-mode driver that is used to provide 32-bit disk access for these controllers.

      Restart Windows and press F8 at the "Starting Windows xx" message, and then choose Logged (/Bootlog.txt) start from the Windows Startup Menu. Examine the just-created Bootlog.txt file to determine if the driver listed above is loading properly.

      In Windows 98, press and hold the CTRL key until you see the Windows 98 Startup menu, and then choose Logged (/Bootlog.txt).

      If the Bootlog.txt file shows an "Init Failure" or "Load Failure" message for the driver listed above, proceed with step D. If the Bootlog.txt file shows an "INITCOMPLETESUCCESS" message for the drive listed above, examine the IOS.LOG file.

      Windows creates an Ios.log file in the Windows directory if any drives are using MS-DOS Compatibility mode. The first few lines of the Ios.log file may contain information describing why the protected-mode disk driver failed to load. Please have this information available if you contact Microsoft Product Support Services about this behavior.
    4. Check for the NOIDE value in the registry under:


      The NOIDE value is placed in the registry when the protected-mode driver for the IDE Controller is not properly initialized.
      For additional information about how to troubleshoot NOIDE, click the article number below to view the article in the Microsoft Knowledge Base:
      151911 MS-DOS Compatibility Mode Problems with PCI IDE Controllers
    5. Make sure the protected-mode driver is not damaged.

      For all ESDI and IDE drives, Windows uses ESDI_506.PDR in the IOSUBSYS directory to provide 32-bit disk access. For SCSI controllers, Windows uses SCSIPORT.PDR and a "mini-port" (.MPD) driver to provide 32-bit disk access.

      Manually extract the appropriate .pdr or .mpd files from the Windows disks or CD-ROM, or run Setup and choose the Verify option.
  5. Check to see if the Mh32bit.386 driver is being loaded in the System.ini file. Check for a line that reads "device=mh32bit.386." This driver is installed by MicroHouse EZ-Drive software, and is not compatible with the Windows protected-mode disk drivers. This driver is not removed by Windows Setup.
  6. Contact the hard disk controller's manufacturer for information about Windows compatibility. You may be able to get protected-mode, 32-bit disk access in Windows by using one of the following methods:

    • Disable any enhanced features (such as caching, fast or turbo mode, reduced data transfer rates, and so on) on the controller (SCSI, IDE, or ESDI) or system BIOS (IDE only).
    • Obtain a protected-mode Windows disk driver, or Windows 3.1 FastDisk driver for the controller.
A real-mode driver is "safe" if its functionality does not exceed thefunctionality of the corresponding Windows protected-mode driver. If areal-mode driver is safe, the protected-mode driver can take over all I/Ooperations for the corresponding device. Otherwise, Windows routes allI/O operations through the real-mode driver.

An example of an unsafe driver is a real-mode IDE/ESDI driver that usesdynamic encryption for security reasons. Since Windows does not provideencryption, Windows does not enable the protected-mode IDE/ESDI driverto take over the real-mode driver. Any real-mode driver with functionalityon the following list is considered unsafe:

  • Data compression that is not compatible with DoubleSpace
  • Data encryption
  • Disk mirroring
  • Bad sector mapping
  • Fault tolerance (for example, maintenance of ECC correction on a separate disk)
  • Vendor-specific IOCTLs
  • Microsoft-defined IOCTLs with vendor-extended features
The safe driver list (the Ios.ini file) is a Windows-maintained list ofsafe drivers. Each entry in the list identifies a driver or TSR thatWindows can take over with the corresponding protected-mode driver. Thesafe driver list includes the name of the driver or TSR. This name shouldbe the same as the name in the Config.sys or Autoexec.bat file.

Windows does not store the version number of the driver or TSR in thelist, so it is the responsibility of the vendor to change the name of thedriver if a future version of the driver is enhanced in a manner thatmakes the driver unsafe.

By default, the following drivers are considered safe:
  • MS-DOS 5.0-compatible real-mode block device drivers
  • INT 13 monitors (hooks INT 13 for monitoring INT 13 I/O but does not access the hardware directly or modify the I/O buffer)
  • INT 13 hooker (hooks INT 13 for altering INT 13 I/O but does not access the hardware directly)
  • INT 13 driver (provides INT 13 functionality and directly accesses the hardware)
  • ASPI Manager (implements ASPI for MS-DOS specification)
  • CAM Manager (implements MS-DOS CAM specification)
NOTE: If the real-mode driver you are using has better performance or provides some functions that are not be present in the Windowsprotected-mode driver, the driver's vendor should remove the driver fromthe safe driver list. The system may use real mode to access the drive.If the real-mode driver you are using can be safely taken over byprotected-mode drivers, the driver's vendor can add that driver to thesafe driver list.

Disk Manager is manufactured by OnTrack Computer Systems, a vendorindependent of Microsoft; we make no warranty, implied or otherwise,regarding this product's performance or reliability.

EZ-Drive is manufactured by Micro House, a vendor independent ofMicrosoft; we make no warranty, implied or otherwise, regarding thisproduct's performance or reliability.
ez.exe dm.exe dmdrvr.bin xbios.ovl tshoot noide w95hwfaq win95 win98 win98se winMe winMil Drvdata bin Drvidx bootlog txt config sys or autoexec bat

Article ID: 130179 - Last Review: 01/19/2007 04:56:50 - Revision: 1.4

  • Microsoft Windows 95
  • Microsoft Windows 98 Standard Edition
  • Microsoft Windows 98 Second Edition
  • Microsoft Windows Millennium Edition
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