INT 15H 81H: Device Close

                                                                        [AT]
 Expects: AH    81H
          BX    device ID
          CX    process ID
          CF    NC (0) (clear the Carry Flag before when invoking this fn)
          ──────────────────────────────────────────────────────────────────
 Returns: AX    0081H
          ──────────────────────────────────────────────────────────────────
    Info: This service is designed to be intercepted by a multitasking
          operating system.  It would be used, along with INT 15H fns 80H
          and 82H to avoid device conflicts.

          When unintercepted, the BIOS simply sets AH to 0 and clears CF.

See Also: INT 15H (extended AT services)
          BIOS Data Area
          ROM-BIOS Functions
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