Monday 6 April 2015

Remembering... The Parallel Port

Parallel Port

David Hayward talks about his favourite connection on the back of a PC

Long before we had these new-fangled USB connections, there were just two choices for hooking up a printer or scanner to your PC: serial and parallel. (Of course, there are three if you include networking.)

Serial was a small, nine-pin port (mostly, although there were other examples) that looked very much like a VGA port, which is why being a techie in the 90s you often found someone complaining of a faulty monitor with the PC end of the VGA cable plugged into the serial port.


Parallel, on the other hand, was unmistakable. With its long, often purple-coloured, 25-pin port taking up the majority of space on the rear of the PC, there was something reliably solid and reassuring about it. How often have we been asked 'Where does the printer plug into?' and answered with. The only place that connection is going to fit!'?

The parallel port was king, and it allowed us to connect not just printers but also scanners, external drives, modems, weather stations, those weird-looking devices that allowed you to program chips and boot ROMs, software DRM-like protection as dongles. And, of course, with help from the saviour of the PC technician, Laplink, we could connect two PCs and send files to and from each.

Its History

The parallel port was developed in 1970 by a group of people who worked at Centronics - hence why it was also known as a Centronics Port. Dr An Wang, Robert Howard and Prentice Robinson developed the parallel port standard as a means to connect their new line of printers, calculators, VAX systems and the like.

Later, IBM started to use the port as the standard on its PCs, but with some small differences to better cope with emerging printers and other peripherals. The 25-pin port on the PC side was then married to the 36-pin unique connector on the opposite end of the cable and thus became the PC-to-printer cable that could send 8-bits of data parallel to each other, to a maximum speed of around 100KB per second.

As the peripherals being attached to PCs became more powerful and the need for greater speeds with a higher level of stability was the norm, HP then improved the parallel connection and introduced a bidirectional standard in the early 90s.

The parallel port surprisingly lasted for quite some time before being put to rest by the introduction of USB in the mid to late 90s. But even though USB was faster, cheaper and made a better connection, the parallel port was still a regular on the backs of motherboards for many more years.

These days you'll be lucky to find a motherboard with a parallel port. Usually there's a parallel-to-USB connection somewhere along the line, or you could pick up a PCI parallel port card from a specialist supplier.

The Good

Being able to find the port in the dark, under a desk, while holding your breathe to prevent inhaling clouds of dust.

Wonderful Laplink speeds and a solid connection for whatever it was you were running.

The Bad

Big cables - very big, chunky, heavy and painful when they land on your head from the around the back of a desk.

Someone trying to hook up a printer remotely using someone else's dodgy home-made parallel cable.

Conclusion

The parallel port brought us the kinds of connectivity, including multiplayer games, that you could only manage in a network. And remember, this was before we had home networks, routers and all that modern stuff.

Did You Know...

• Pin 1 carries the strobe signal. It maintains a level of between 2.8V and 5V but drops below 0.5V whenever the computer sends a byte of data. This drop in voltage tells the printer that data is being sent.
• The Enhanced Parallel Port (EPP) could transmit data at an astounding maximum of 2MB per second.
• We once saw a device that was hooked up to a nuclear submarine (we don't know what it was doing), via a parallel port on a PC.
• At that same shipyard, there was also a huge CNC machine making armour plating for tanks hooked up via a parallel port. Fascinating stuff.
• We made a rope swing out of old Centronics cables once. It's probably still there today!