Here's a thumbnail sketch of how Version 2.0 came to be. As a child of the Sixties who somehow managed to grow up without a Digi-Comp, I stumbled upon it only recently, in the course of researching educational toys of the past. There it was in a 1968 Childcraft catalog salvaged from my parents' attic, at the tantalizing price of $5.95 (about $35 in today's coinage). With curiosity piqued, I started checking eBay listings. Thirty years out of production and apparently something of a collector's item, a few old Digi-Comps were turning up every month but typically selling in the $150 range—a far cry from $5.95 or even $35. For some months I kept checking back—and one day a listing happened to mention the existence of a Yahoo group called FriendsOfDigiComp. That was the turning point.

A few further clicks revealed that since February 1999, in over a thousand posts, several hundred subscribers to the Yahoo group—mostly middle-aged men, it would seem—had been sharing their reminiscences of geeky Sixties childhoods, subsequent careers in computing and allied fields, and dreams of reacquiring (or maybe even remanufacturing) a certain favorite toy that they'd all had in common.

Digi-Comp I first appeared under America's Christmas trees in 1963 as a cardboard box emblazoned with the words "first real operating digital computer in plastic." Inside were an assortment of styrene plates in red and white, a dozen wire rods, some rubber bands and plastic tubes. Following along in the assembly instructions, you snapped the pieces together to produce a sturdy replica of the strange-looking contraption depicted on the box. OK, so now you'd built a "computer"-how the heck did it "work"? With some prodding and tugging, you could make it emit some clacking sounds, but the three digits in the readout window stayed locked at "000".

So at that point, you either gave up or, impelled by curiosity—or maybe some predisposition to follow instructions that other kids lacked—opened the accompanying manual. And perhaps also a new door in your life...

I was eleven years old (53 now) when I received a Digi-Comp I for Christmas. I was fascinated with it from a mechanical standpoint and played with it for hours. Even when I had mastered all the programs, I would still get it out and see what it could do. I played with it off and on for a couple of years until it wore out or broke, can't remember which. I think of it as the spark that got me interested in computing, a career that has been and remains a lot of fun.
[knuck1723: Message 885, Jan 27, 2005]

I was given a Digi-Comp I as a child, but I'm not sure of the exact date. It was sold in the UK by I-Cor of 18 Stamford Hill, London N16. I sent a program to ESR as I was invited to do on p.47 of the "Detailed Programming" manual, and waited for my $10, but I have not heard from them yet.
[david_susx: Message 117, Oct 4, 1999]

My uncle began to teach me about mainframes, showed me Gunner-IV on the GE Timesharing network via teletype and around that time I got a Digi-Comp I. I also began designing primitive switch based computers using multi-pole switches and relays. I tried the old wire wrapped around a nail with tin can contacts all connected directly to house current. Boy were my parents mad. The Digi-Comp was a lot simpler to work with. I think the mystery of how it really worked stayed with me and has only now been solved.
[maverick_78726: Message 167, Mar 6, 2000]

My most quixotic programming effort ever was trying to program perfect tic-tac-toe on my Digi-Comp I in 6th grade. Before I started, I realized tic-tac-toe was a never-lose game with the right strategy. I discovered the rotation and reflection symmetries of the game right away, but I never cottoned on to the fact that there just wasn't enough memory in old Digi-Comp to get the job done. I filled up a whole sheet of posterboard with the game tree, though.
[colloquialdotcom: Message 298, Jan 29, 2001]

Speed-reading through years of these posts archived in the Yahoo group, I discovered much more than shared personal recollections. For example, some contributors had diligently pursued leads to learn more about ESR (Education Science Research), the small New Jersey-based company that introduced Digi-Comp along with several other educational toys in the Sixties, and then folded. One message shared a communication from an ESR founder:

Irv Lieberman was the guy with the original idea to construct a mechanical digital computer. He worked with Bill Duerig and Dave Hogan at the same company. Bill and Dave helped him to improve the idea and build a working model for the annual March NYC toy fair. The original model used six circular planes with clock rods on the perimeter and was about 1 ft in diameter. Sears became interested but wanted a simpler model. So they redesigned into the form we know today. Irv was bothered by the simplification because it reduced the problem set significantly but he came up with some pretty cool problems in the booklet. The redesigned Digi-Comp was built within hours using stiff paper material and shown to the Sears buyer again who said he liked it. They then found a plastics engineer who helped create the production Digi-Comp I and the company had its first product. ... They eventually sold 250,000 Digi-Comp I machines.
[maverick_78726: Message 178 (based on letter from Bill Duerig), Mar 15, 2000]

In addition to their message archives, the Friends of Digi-Comp had accumulated a great repository of digital files: scans of the original assembly instructions and manual, photos of the plastic components, detailed specs-everything an inveterate cardboard modeler like myself (still unwilling to pay eBay's going rate) needed to start building a working model. Several knife blades later, with a somewhat wobbly prototype in front of me, it was time for a test drive: attaching four tubes to four tabs to create a simple routine that toggled one of the readout digits between 0 and 1 with each clock cycle. The gizmo worked! (And in fact you'll be trying the same thing yourself quite soon, as Experiment 1 in the rewritten manual's Lab section.) At least half the fun was figuring out the ingenious inner workings of the mechanism itself.

For youngsters of the Sixties to whom the word "computer" conjured up room-size machines with tape drives and punched cards, this first brush with digital logic must have left a lasting impression. For me, a programmer/author of later microcomputer and multimedia eras, the fascination was being able to literally create code "by hand" on a mechanical computer. The more I worked through various programming examples, the more I realized that Digi-Comp wasn't so much a computer as a little logic machine. The principles it embodies, like AND and OR gates and Boolean algebra, are still fundamental to digital circuitry after all these years. And the best thing about Digi-Comp is that it makes such concepts tangible and visible— exactly as its inventors intended. It's a rare educational toy whose lessons endure this long.

This new edition of Digi-Comp I is dedicated to the members of FriendsOfDigiComp, without whose communications and contributions it simply would not have been possible. Over the years they've floated many ideas for reissuing Digi-Comp in one form or another. I've taken a different approach with this cardboard kit, and have rewritten the manual from the ground up, but they were clearly onto something—and their collective enthusiasm bolstered my own conviction that Digi-Comp deserved a new lease on life. In a sense the effort was undertaken, unbeknownst and unbidden, for this group of devotees. And with the new version out in the world, their Yahoo forum remains the best place to go to continue the discussion. There is still much of the Digi-Comp and ESR story that remains to be told... new users to enlighten... and new problems to invent and solve.


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