Centronics Parallel Port

This was the standard parallel interface on most computers in the 1990’s. It was originally designed by the centronics group as a printer interface system.
It has now gone on to be used for scanners, removable drives, and robotics interface. Although pretty much superceded by the USB port, it was one of the simplest places to connect something to a computer, the GPIO of the time.

I would advise optically isolating any connections - and never drawing power for more than a few LED’s from the port.