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How Windows Setup Detects CD-ROM Drives

This article was previously published under Q151550
This article has been archived. It is offered "as is" and will no longer be updated.
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This articles discusses how Windows detects CD-ROM drives. Note that all references to real mode support in this article do not apply to Windows Millennium Edition (Me) because Windows Me does not provide real mode support.
Windows detects proprietary, SCSI, and IDE CD-ROM drives differently.The following sections explain the differences.

Proprietary CD-ROM Drives

Windows detects Sony, Mitsumi, and Panasonic proprietary CD-ROMcontrollers directly. Once the controller card is detected, the CD-ROMdrive appears as a child device of that card.

If Windows does not detect one of these drives correctly, it may bebecause the drive is set to an I/O address that Windows cannot check.


If the SCSI host adapter is on an enumerable bus (such as a PCI bus),Windows enumerates it during the first boot after Setup. Otherwise,Windows detects the SCSI adapter during Setup. After the SCSIcontroller is working properly, the SCSI enumerator looks for devices(such as CD-ROM drives) on the adapter.


SCSI II CD-ROM drives access data CD-ROMs and audio CDs in protected mode.


SCSI I CD-ROM drives use protected-mode drivers only if no real-moderivers are loaded. The protected-mode drivers give you access to dataCD-ROMs only.


Windows must detect the IDE controller before it can detect the CD-ROMdrive. After the IDE controller is working properly, the IDE enumeratorlooks for devices (such as CD-ROM drives) on the controller.

Additional Information

  • In some cases, the real-mode drivers for the CD-ROM drive must be loaded in the Config.sys and Autoexec.bat files in order for Windows to successfully detect the CD-ROM drive. For additional information, please see the following article in the Microsoft Knowledge Base:
    ARTICLE-ID: 131499
    TITLE : CD-ROM Drives Requiring Real-Mode Drivers
  • Before Setup examines the computer for installed hardware, it may ask if you have a CD-ROM drive. Setup prompts you for this information only when it cannot find traces (such as CD-ROM drivers in memory) of a proprietary CD-ROM drive. If Setup finds the information, it does not prompt you for this information.

    Windows Setup gives you the opportunity to skip the detection of a CD-ROM drive if you do not have one to save time during Setup.
  • You may be prompted whether there is a CD-ROM drive even when you run Setup from a CD-ROM drive. Setup does this because it needs to know the hardware configuration of the CD-ROM drive. Simply finding Mscdex.exe in the Autoexec.bat file does not provide this information; Setup must still perform detection.
  • After it detects a CD-ROM drive, Setup may leave the CD-ROM device driver in the Config.sys file and remark out Mscdex.exe in the Autoexec.bat file. Although the CD-ROM device driver is loading from the Config.sys file, a protected-mode Windows driver takes over the real-mode driver.

Article ID: 151550 - Last Review: 12/04/2015 14:47:16 - Revision: 2.1

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

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