DEC H-500 Computer Lab

Manufactured By: Digital Equipment Corporation

Designed By: John L. Hughes

Release Date: 1968

Many people reading this will be familiar with the Digital Equipment Corporation (DEC) lines of PDP machines. I would guess though that far fewer have encountered the H-500 Computer Lab. Designed by John Hughes at DEC Canada, and launched in the late 60's, the H-500 was part of a COMPUTER LAB curriculum to introduce students and engineers to digital electronics. It's not surprising that DEC would undertake this since more than half of it's PDP machines at the time were installed in educational institutions.

The machine itself shipped with a wonderful Computer Lab Workbook, written by the designer, that contained a complete course in digital electronics. Together the COMPUTER LAB package was intended to accompany courses in binary arithmetic, Boolean algebra, digital logic or computer technology. While not a true computer, the H-500 could be "wired" to perform many of the underlying operations of a true computer using a point-to-point patch cord mechanism.

It felt like this build took a really long time, but in fact it was only three months of effort. There were frustrating part delivery delays due to Covid-19, and not having access to my local maker space slowed me down a bit and forced me to get creative, but all things considered I'm OK with how it went. It was nice to have something interesting to work on during this enforced "quiet time".

A short time after I published my H-500 build instructions I was honored to receive an Email from John Hughes the designer of the H-500 and author of the Computer Lab Workbook. Here is part of what he wrote:

By my recollection, about 4500 – 5000 Computer Labs were built over the life of the product. Almost all were sold to the technical education market to be used as the practical lab part of a course on digital and computer logic. Over the usable life of the product, my guess is that an average of 20 students (or more) would get to use each Computer Lab. That translates to a worldwide population of as many as 90,000+ technicians and engineers who gained their first practical lab experience with digital logic on a DEC Computer Lab.

With John's permission the full Email can be found here.

As the 60s drew to a close devices like the DEC H-500 became a lot less toy like and much more practical and educational.