DOS Fn 0eH: Select DOS Default Disk

                                                         Compatibility: 1.0+ 
 Expects: AH    0eH
          DL    drive number (0=A, 1=B, etc.) to become the default disk
 Returns: AL    total number of system drives
    Info: The drive identified in DL becomes the current DOS default drive
          (if it is a valid drive number).

          Error test; use DOS Fn 19H (Get CurDisk) to make sure it worked.

   Notes: ■ The return value in AL is number of drives of any type,
            including hard disks and 'logical' and phantom drives (such as
            drive B: in a 1-floppy system).

          ■ The return value is simply a count of valid drive IDs--not an
            indication of which drive IDs are valid.

          ■ This call triggers a critical error (INT 24H) when you select a
            drive that does not contain a diskette.

Versions: DOS 3.0+ AL is the same as the value of LASTDRIVE=, as specified
          in CONFIG.SYS.  The a typical default LASTDRIVE is 5.

See Also: 3bH (set default directory
          INT 11H (equipment check)
          INT 24H (critical error handler)
          Directory and File Functions
          DOS Functions