Updated: 04/26/2017 by Computer Hope

standard parallel portAlternatively referred to as SPP (Standard Parallel Port), unidirectional refers to data either sent or received in one direction. For example, the parallel port on a computer can be set to unidirectional, allowing the computer to send data to a printer but not allow that printer to communicate back to the computer.

Unidirectional ports were found on computers manufactured before 1995, capable of transmitting data 4-bits at a time, at 40 to 60 KBps over a six foot cable. This standard was later moved into the IEEE-1284, updated, and now known as Centronics mode.

Bidirectional, Centronics mode, Parallel port, Printing terms