Drive C is using MS-DOS compatibility mode file system

The above problem can haunt Windows 9x systems. When this happens, it seems that CD-ROM drives will no longer function or appear at all in My Computer.

The fix isn't straight forward. Because it has been years since Microsoft has supported a Windows 9x product, and the Knowledge Base articles that discussed this issue have since been removed.

Below you will find the Knowledge Base article that discusses some potential fixes to this issue. Hope this helps other people that still set up ancient systems or use emulation software like 86box.

MS Knowledge Base, article Q151911

MS-DOS Compatibility Mode Problems with PCI IDE Controllers

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The information in this article applies to:

Microsoft Windows 95

Microsoft Windows 95 OEM Service Release, versions 2, 2.1

Microsoft Windows 98

Microsoft Windows 98 Second Edition

Microsoft Windows Millennium Edition

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If this article does not describe your hardware-related issue, please see the following Microsoft Web site to view more articles about hardware:

http://support.microsoft.com/support/windows/topics/hardware/hwddresctr.asp

IMPORTANT: This article contains information about editing the registry. Before you edit the registry, make sure you understand how to restore it if a problem occurs. For information about how to do this, view the "Restoring the Registry" Help topic in Regedit.exe or the "Restoring a Registry Key" Help topic in Regedt32.exe.

SYMPTOMS

If your computer contains a Peripheral Component Interconnect (PCI) Integrated Drive Electronics (IDE) hard disk controller that employs serialization between the two IDE channels, you may experience the following behaviors:

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

-and-

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

If you uninstall and then reinstall the hard disk controller, this behavior is not resolved.

CAUSE

This behavior can occur if the protected-mode driver for the hard disk controller is not properly initialized when you start Windows. When this occurs, a NOIDE value is placed in the registry which prevents Windows from making future attempts to initialize the protected-mode driver.

RESOLUTION

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

For information about how to edit the registry, view the "Changing Keys and Values" Help topic in Registry Editor (Regedit.exe) or the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in Regedt32.exe. Note that you should back up the registry before you edit it. If you are running Windows NT or Windows 2000, you should also update your Emergency Repair Disk (ERD).

NOTE: The purpose of the registry value that is mentioned in this section is to prevent damaged data. Before you modify this registry value, it is recommended that you perform the troubleshooting steps in the following Microsoft Knowledge Base article:

Q130179 Troubleshooting MS-DOS Compatibility Mode on Hard Disks

All Versions

To cause Windows to attempt to reinitialize the protected-mode IDE driver:

Click Start, click Run, type regedit in the Open box, and then press ENTER.

Locate and click the following registry key:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\VxD\IOS

In the right pane, right-click the NOIDE value, and then click Delete.

Quit Registry Editor.

After you update the registry, restart Windows. Windows attempts to initialize the protected-mode driver for the controller. If Windows can initialize the protected-mode driver for the controller, the file system and virtual memory operate in 32-bit mode and Device Manager does not display an exclamation point in a yellow circle for the IDE channels.

If the protected-mode driver is not initialized properly, you receive an error message and the NOIDE value is re-created. Windows uses the MS-DOS Compatibility mode file system the next time that you start the computer.

Windows 98 Only

If you are running Windows 98 on your computer, locate the Tools\Mtsutil folder on the Windows 98 CD-ROM, right-click the Noide.inf file, and then click Install. When you do this, the NOIDE value is deleted if it exists. After you use this file, restart your computer.

MORE INFORMATION

This issue can occur if your computer has an IDE controller that requires serialization between the primary and secondary IDE channels. The protected-mode drivers for these IDE controllers may not be initialized if one of the following situations occurs:

If one IDE channel has a supported hard disk, and the second channel has a CD-ROM or another type of drive that requires Real-mode drivers. Because there must be serialization between the two IDE channels, Windows cannot access the hard disk in Protected mode and use the other device in Real mode. When this occurs, the Protected-mode driver is not initialized and the NOIDE switch is placed in the registry to prevent future errors. Both disk devices can then operate in Real mode.

-or-

If you manually remove the driver for the IDE controller from Device Manager and then reinstall it, or if you disable and then re-enable the protected-mode driver. Some PCI controller drivers are not designed for dynamic enabling and disabling, and can cause the Protected-mode driver to not initialize properly.

The Windows device drivers for the following controllers may cause 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

Ali M5229 PCI Busmaster IDE Controller

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