All about the (PC) Parallel Port (Centronics, IBM, HP, Iomega...)

An interesting historical and technical take on the humble parallel port: from parallel, to Centronics, to EPP and ECP and IEEE 1284.

Here’s a snippet or two:

With the inexpensive and small Centronics 101 a printer was, for the first time, a peripheral you could buy at the store and connect to your existing computer.

Centronics was an interesting company to make a printing breakthrough. Effectively a division of Wang (best known for their CRT word processors), Centronics had originally built special terminals for casino cashiers. […] the Centronics dot-matrix impact head was originally developed as a faster, smaller print head for these slip printers. As sometimes happens with innovations, this new form of high-speed printer with simplified head […] became a more interesting idea than the rest of the terminal.

Centronics was not a printer company, and did not have the expertise to develop a complete printer. To close this gap they entered a partnership with Brother International, the US arm of Japanese typewriter (and sewing machine) maker Brother, whose president incidentally lived next door to the president of Centronics. And thus came about the Centronics 101, with the print head and control electronics by Centronics and basically all other components by Brother based on their typewriter designs.

Centronics was getting this printer together quickly, with an aim towards low cost, and so they stuck to what was convenient… and incidentally, they had a significant backstock of 36-pin micro-ribbon connectors on hand. This style of connector was mostly used in the telecom industry […]

And so, largely by coincidence, the Centronics 101 was fitted with the 36-pin micro-ribbon (also called Amphenol or CHAMP after telecom manufacturers) connector that we now call the Centronics interface.

About the evolution of the interface:

The four printer control pins provided by Centronics were rather limited and more sophisticated printers had more complex information to report. To address this need, HP (which had adapted the Centronics interface nearly from the start of their desktop printers) re-invented IBM’s simpler bidirectional arrangement in 1993. The HP “bi-tronics” standard once again made the four printer pins a general purpose data bus. Since the computer already needed the hardware to monitor these four pins, bi-tronics was compatible with existing Centronics-style printer controllers.


Nice history stuff. For more technical details, there is Jan Axelson’s book “Parallel Port Complete” (

I’ve always liked Jan’s stuff - she does a good job of covering the material in a way that is educational, and yet is a good read.