Opening and Closing a Parallel Port
Clients can share a parallel port. A client must open a file on a parallel port before the client can use other I/O requests or use the parallel port callback routines. A client must not attempt to communicate with a parallel port after the client has closed its file on the port.
Note that in a Plug and Play environment, a device can be removed or added whenever there are no open files on it. In general, every time a parallel port is added, Plug and Play assigns a different location and resources.