The Standard Parallel Port (SPP) is a printer port developed by IBM in the early 1980s to support unidirectional operation between computers and printers. It was the standard mode of operation for the Centronics interface, which is still sometimes used.
The parallel port is increasingly being replaced by the USB interface or Ethernet networks. Because of the unidirectional operation, there are no status messages from the printer back to the computer with this parallel interface.
With theIEEE1284 standard, IEEE has standardized a bidirectionally operating parallel port, via which simultaneous data exchange between computer and printer and between printer and computer is possible. The data transfer speeds ofthe standard parallel port are between 100 kB/s and 300 kB/s, those of the IEEE 1284 parallel interface are 1.5 MB/s, and those of the bidirectional extensions, the Enhanced Parallel Port( EPP) and the Extended Capability Port( ECP), are 2 MB/s.