bidirectional parallel port

One significant features of the Laserjet 4 is its bidirectional parallel port.

With the introduction of the PS/2 in 1987, IBM offered a new bidirectional parallel port design.

This data is then processed with some proprietary algorithm to correct for different exposure conditions, and sent to the computer via the device's input/output interface (usually USB, previous to which was SCSI or bidirectional parallel port in older units).