The Designer of the Original H-500 Computer Lab Reaches Out

A project log for DEC H-500 Computer Lab Reproduction

Reproduce the Digital Computer Lab H-500, a training tool from the late 60's aimed at teaching people the basics of logic circuits.

Michael GardiMichael Gardi 10/30/2020 at 21:370 Comments

I was honored to receive an Email from John Hughes the designer of the H-500 and author of the Computer Lab Workbook. With John's permission I would like to share that Email as it contains valuable historical insight into the project. John wrote....


More than 50 years after I designed the Digital Equipment H500 Computer Lab and wrote the Computer Lab Workbook, it’s incredible to see that you have created a totally functional copy of the product.  Congratulations on an extremely well executed project.  Looking at the web pictures and videos I would have thought your Computer Lab had been made at DEC Kanata many years ago.

Since many of the folks looking at your Computer Lab copy likely have used a DEC Computer Lab at some point in their technical education, here’s a little relevant DEC history that you might find interesting.

In the mid 60’s DEC brought out a logic training system called the Logic Lab that used the discrete component logic modules that at the time were the building blocks of all computers.  The Logic Lab was very flexible and powerful.  In fact, DEC engineers used multiple Logic Labs to prototype the first PDP‑8S computer.  The biggest problem with that prototype was suppressing the electrical noise associated with long leads and multiple Logic Lab chassis (and power supplies) – eventually though it worked.

By the late 60’s integrated circuit logic devices had displaced discrete device logic modules as computer building blocks.  Add to that a Logic Lab base price of over $2,000 and that was well above the budget of many tech schools and universities – it was time for a replacement product.

Denny Doyle, the President of DEC Canada, wanted a locally developed and manufactured product to expand the role of the Canadian subsidiary.  About that time, I joined Digital Equipment Canada as a relatively newly‑minted electrical engineer.  Shortly after I was tasked with designing and writing a book to support an affordable logic training device for the technical education market based on the then‑popular TTL (Transistor-Transistor Logic) integrated circuits.  The result was the H500 Computer Lab manufactured by Digital Canada that sold for $400 back in the late 60’s through the early 80’s.

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. 

The Computer Lab Workbook was key to the success of the product.  It was an inexpensive paperback handbook that DEC printed in volume and distributed free of charge for product promotion (along with many other DEC handbooks).  The book was a ready-to-use lab course for computer logic – that clearly appealed to educators.  The first printing of the book, 100,000 copies, was gone quickly in about a year.  A second printing of 100,000 was used up much more slowly and lasted for the remainder of the product life.

DEC sold a separate Computer Lab Teacher’s Guide written by Larry DeAngelo.  It had answers to questions in the Computer Lab Workbook along with additional experiments and supporting material.

The advent of bipolar integrated circuits created a very large market to train engineers and technicians to design and maintain computers and digital electronic devices, including computers.  Based on what I have read since, the Computer Lab was the market leading device to provide a practical lab experience to support that training in North America and Europe through the 70’s and early 80’s.

Integrated circuit technology has packed ever increasing functionality and performance at ever decreasing cost into a single device.  A hobbyist today can purchase a full computer with storage and I/O on a small PC board for less than $50 on Amazon.  Programming low cost chip processors has replaced logic design as the way to create unique products.  Even so, the Computer Lab had a remarkably long run in a market with very fast changing technology.

Over 50 years after they were manufactured, Computer Labs still regularly appear for sale on  Interestingly, surfing the web a while ago someone mentioned a still in service Computer Lab as recently as 2006 in Switzerland. 

Mike, your creation of a Computer Lab copy is really cool.  Again congratulations for a project extremely well done.  Now there are two of us who have both designed and built Computer Labs … a little over 50 years apart.


John L Hughes