4825SX (250-5141/42) Parallel Faxback Doc. # 1696 The 25-pin parallel port is located on the back of the computer. See the "Using the Computer" section for instructions on how to connect a parallel device. The parallel port on the computer allows either one-way or two-way data transfer. In unidirectional transfer, the computer uses the port only to send data to the parallel device. In bidirectional transfer, the computer uses the port both to send output to the parallel device and to receive input from the device.