BUG: MSCDEX May Not Detect Disk Change

• Microsoft CD-ROM Extensions (MSCDEX) for MS-DOS, versions 2.0, 2.1, 2.2, 2.21, 2.22, 2.23
• Microsoft Windows Software Development Kit (SDK), version 3.1

SYMPTOMS

If a GetAttributes function call is the first MS-DOS API call made following a CD-ROM disk change, MSCDEX doesn't detect that the disk is changed, so the function call reflects the contents of the previous disk. The next Open, Search, or Change Directory function call will cause MSCDEX to detect the disk change.

CAUSE

The MSCDEX driver fails to issue a Media Check call to the Hardware Dependent Device Driver when the GetAttributes call is made.

WORKAROUND

You can check for a CD-ROM ID file by using the C-Runtime access() function or by making direct calls to the MS-DOS Interrupt 21h. Function AX=4300h should be changed to use a file open call. Windows Applications that use the SDK OpenFile() function to detect a key file should be changed to use _lopen().

STATUS

Microsoft has confirmed this to be a problem in the MSCDEX versions listed at the beginning of this article. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

The OpenFile() function in the Microsoft Windows version 3.1 SDK makes a GetAttributes function call prior to opening a file for reading if the system is running with Novell Netware loaded. The OpenFile() function fails if the GetAttributes() function fails to find the requested file. As a result, if the OpenFile() function is used to detect which CD-ROM is in the drive by opening a key file, the wrong CD-ROM may be detected following a disk change.

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