Function 0Eh (14)        Select Default Drive

    Sets the default drive and returns the number of logical drives in the
    system.

       On entry:      AH         0Eh
                      DL         Drive number (0=A, 1=B, etc.)

       Returns:       AL         Number of logical drives in system

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       Notes:         The floppy disk on a single floppy system is counted
                      as two logical drives, A: and B:.

                      DOS 3 and later versions report a minimum of 5
                      logical drives, unless the CONFIG.SYS file contains
                      a LASTDRIVE statement.

                      To determine the number of physical floppy drives on
                      the system, use Interrupt 11h (17). To determine the
                      number of physical hard drives, use Interrupt 13h,
                      Function 8.