PRB: Network Drive Type Reported Incorrectly

• Microsoft Windows Device Driver Kit (DDK) for Windows versions 3.0 and 3.1

SYMPTOMS

In versions 3.0 and 3.1 of the Microsoft Windows graphical environment, the Windows File Manager and the GetDriveType() API reports that some network drives are local fixed drives.

CAUSE

In some releases of PC-DOS version 4.00 and MS-DOS version 4.01, Interrupt 21h Function 4409h does not reliably return drive type information.

RESOLUTION

The redirection entry list must store the local drive name in uppercase letters.

MORE INFORMATION

To work around the Interrupt 21h Function 4409h problem, Windows 3.0 or 3.1 recognizes that it is running on PC-DOS 4.00 or MS-DOS 4.01 and uses Interrupt 21h Function 5F02h (Get Redir List Entry) to determine if a drive is remote or local. Windows compares the drive index (A = 0, B = 1, ..., Z = 25) to the drive index returned by the function. Windows also assumes that the drive letter is uppercase.

If lpszLocal points to the "local" name returned by Get Redir List Entry, Windows uses the following algorithm:

    if ((lpszLocal[0] - 0x41) == wListIndex)
    {
        /** drive is remote **/
    }

    else
    {
        /** drive is fixed **/
    }