Troubleshooting MS-DOS Compatibility Mode on Hard Disks

• Microsoft Windows 95
• Microsoft Windows 98

SYMPTOMS

The Performance tab in System properties shows that one or more of the hard disks in your computer is using MS-DOS Compatibility mode. MS-DOS compatibility mode may be in use for either the file system or for virtual memory. You may receive the following message:

Compatibility Mode Paging reduces overall system performance

CAUSE

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 95 loaded.



• The hard disk controller in your computer was not detected by Windows 95.



• 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 95 protected-mode driver is missing or damaged.



• The Windows 95 32-bit protected-mode disk drivers detected an unsupportable configuration or incompatible hardware.

RESOLUTION

To correct the problem, follow these steps:

1. 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.
   
   
   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 95 protected-mode disk drivers.
      
      For information about real-mode geometry translation software that is compatible with Windows 95 protected-mode disk drivers, please see the following article in the Microsoft Knowledge Base:

      ARTICLE-ID: Q126855
      TITLE : Windows 95 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 95 and Microsoft Plus!, Disk Manager 7.04 or later must be used. For more information, please see the following article in the Microsoft Knowledge Base:

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

      
      For information about detecting and removing boot-sector viruses, please see the following articles in the Microsoft Knowledge Base:

      ARTICLE-ID: Q82923
      TITLE : Methods to Detect a Boot-Sector Virus
      
      ARTICLE-ID: Q129972
      TITLE : Description of Computer Viruses
      
      ARTICLE-ID: Q49500
      TITLE : List of Anti-Virus Software Vendors

   
   
   




b. 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 allows protected-mode access in Windows 95.




If no driver is listed on the Performance tab, continue with Step 2.



2. 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 95 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 corresponding to the current hardware profile under Device Usage.



3. 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 missing 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 95 and press F8 at the "Starting Windows 95" message, and then choose Logged (/BOOTLOG.TXT) start from the Windows 95 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 95 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 problem.
   
   
   
   4. Make sure the protected-mode driver is not damaged.
      
      For all ESDI and IDE drives, Windows 95 uses ESDI_506.PDR in the IOSUBSYS directory to provide 32-bit disk access. For SCSI controllers, Windows 95 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 95 disks or CD-ROM, or run Setup and choose the Verify option.
   
   
   



4. 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 95 protected-mode disk drivers. This driver is not removed by Windows 95 Setup.



5. Contact the hard disk controller's manufacturer for information about Windows 95 compatibility. You may be able to get protected-mode, 32-bit disk access in Windows 95 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 95 disk driver, or Windows 3.1 FastDisk driver for the controller.
   
   
   

MORE INFORMATION

A real-mode driver is "safe" if its functionality does not exceed the functionality of the corresponding Windows 95 protected-mode driver. If a real-mode driver is safe, the protected-mode driver can take over all I/O operations for the corresponding device. Otherwise, Windows 95 routes all I/O operations through the real-mode driver.

An example of an unsafe driver is a real-mode IDE/ESDI driver that uses dynamic encryption for security reasons. Since Windows 95 does not provide encryption, Windows 95 does not allow the protected-mode IDE/ESDI driver to take over the real-mode driver. Any real-mode driver with functionality on 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

• 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)

Additional query words: ez.exe dm.exe dmdrvr.bin xbios.ovl tshoot noide

Keywords          : kbenv kbhw kbtshoot diskmem win95 win98 cddrive 
Version           : WINDOWS:95
Platform          : WINDOWS 
Issue type        : kbprb 

Last Reviewed: June 28, 1999