Int 15h, 81h            Device Close                                     many

    Provides an interface to close a device with a specific process.

        Entry   AH = 81h
                BX = Device ID
                CX = Process ID

        Return  CF Set if service not supported, else cleared

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    The PC, PCjr, and the XT dated 11/08/82 do not support this
    service.

    This interface is supported for multi-tasking environments, where
    more than one process (or task) may be executing in the system.
    Usually the operating system will supply the handler for this
    service; this way, the operating system can keep track of which
    processes are using each device on the system.

    The operating system will use this service to discontinue the use
    of a device by a process.