MS-DOS Compatibility Mode Problems with PCI-IDE Controllers

ID: Q151911

The information in this article applies to:

Microsoft Windows 98
Microsoft Windows 95
Microsoft Windows 95 OEM Service Release version 2
Microsoft Windows 95 OEM Service Release version 2.1

IMPORTANT: This article contains information about editing the registry. Before you edit the registry, you should first make a backup copy of the registry files (System.dat and User.dat). Both are hidden files in the Windows folder.

SYMPTOMS

If your computer contains a PCI-IDE hard disk controller that employs serialization between the two IDE channels, you may experience the following problems:

32-bit file system access and 32-bit virtual memory are not available.

Device Manager displays an exclamation point in a yellow circle for the primary and secondary IDE channels.

Removing and reinstalling the hard disk controller does not resolve the problem.

CAUSE

The protected-mode driver for the hard disk controller was not properly initialized when you started Windows previously. When this occurs, a NOIDE entry is placed in the registry, preventing Windows from making future attempts to initialize the protected-mode driver.

RESOLUTION

NOTE: The purpose of the registry key mentioned in the RESOLUTION section of this article is to prevent data corruption. Before you change this key, Microsoft recommends you perform the troubleshooting steps listed in the following Microsoft Knowledge Base article:

ARTICLE-ID: Q130179
TITLE : Troubleshooting MS-DOS Compatibility Mode on Hard Disks.

WARNING: Using Registry Editor incorrectly can cause serious problems that may require you to reinstall Windows 95. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk.

NOTE: For information about how to edit the registry, view the Changing Keys And Values online Help topic in Registry Editor (Regedit.exe). Note that you should make a backup copy of the registry files (System.dat and User.dat) before you edit the registry.

To cause Windows to attempt to reinitialize the protected-mode IDE driver, remove the NOIDE entry from the following registry key:

HKEY_LOCAL_MACHINE\SYSTEM\CURRENTCONTROLSET\SERVICES\VXD\IOS

If you are using Windows 98, navigate to the Tools\Mtsutil folder on the Windows 98 CD-ROM, right-click the Noide.inf file, and then click Install. This should remove a NOIDE entry if it exists. After you use this file, restart your computer.

After you update the registry, restart Windows. Windows will then attempt to initialize the protected-mode driver for the controller. If no problems are encountered, the file system and virtual memory will operate in 32-bit mode, and Device Manager will not display an exclamation point in a yellow circle for the IDE channels.

If the protected-mode driver is not initialized properly, an error message will be displayed and the NOIDE registry entry will be re-created. Windows will use the MS-DOS compatibility mode file system the next time you start the computer.

MORE INFORMATION

This problem can occur with an IDE controller that requires serialization between the primary and secondary IDE channels. The protected-mode drivers for these IDE controllers can fail to be initialized if one of the following situations occurs:

One IDE channel has a supported hard disk, and the second channel has a CD-ROM or other type of drive that requires real-mode drivers to be loaded. Because of the serialization between the two IDE channels, it is impossible to access the hard disk in protected mode and use the other device in real mode. This causes the protected-mode driver to fail initialization, and the NOIDE switch is placed in the registry to prevent future errors. Both disk devices then operate in real mode.

The driver for the IDE controller is manually removed from Device Manager and then reinstalled, or the protected-mode driver is disabled and then re-enabled. Some PCI controller drivers are not designed for dynamic enabling and disabling, and can cause the protected-mode driver to fail initialization.

The Windows device drivers for the following controllers are known to exhibit this behavior:

CMD PCI-0640 PCI-IDE controller

Standard Dual PCI-IDE controller

Opti Dual PCI-IDE controller

Intel 82371 AB/EB Pci Bus Master IDE Controller

Other PCI-IDE controllers that use serialization between the IDE channels may also exhibit this behavior.

Additional query words: osr 95


Keywords          : kbenv kbhw osr2 diskmem win95 win98 cddrive 
Version           : WINDOWS:95
Platform          : WINDOWS 
Issue type        : kbprb

Last Reviewed: March 3, 1999