The Hobbyists Who Build Their Own CPUs

Warren Toomey has been involved in some fascinating computer projects. A 2016 blog post describes “Bringing PDP-7 Unix Back to Life” and another one on “on starting a Unix Heritage Society.”

The posts themselves are part of the incredible journey of a 1994 webserver — which had previously hosted a repository of files only accessible via FTP. Its contents have survived all the way into 2022 and are hosted in the cloud on a spacious virtual machine.

And now Toomey’s involved in yet another remarkable mission. He’s maintaining a directory of pages from around the web, each one showcasing a different home-built CPU.

There are 85 different webpages in all, collectively forming a kind of secret society of the world’s most ambitious tinkerers.

The pages have all been assembled together into the Home-Built Computers Web Ring, where each page connects to another one in the series, creating a kind of linked list of webpages. Back before Google, a “webring” used to be a way to collect thematically-similar web sites. Often they led to cohesive communities around a certain topic.

👁 Homebrew Computing Web-ring (screenshot from RISC relay CPU site)

Toomey maintains the master directory, offering a thumbnail icon leading directly to each of the 85 pages.

And that’s certainly the case with Home-Built Computers WebRing, where each page represents somebody’s beloved personal project — and an inspiring story of determination.

A Ring Around the World

The webring’s community is still growing. Back in 2018 there were just 48 members — so it’s nearly doubled in the last four years. And while the WebRing’s main page appears to be hosted in Australia, it lists pages from around the world — and in a variety of states of completion.

For example, the RISC relay CPU page (last updated in 2018) got as far as the testing of home-built arithmetic/logic units and register cards for what it describes as “soldering problems.” But it was already able to run “real programs” on its four 8-bit registers. How? By using a Raspberry Pi board which can download a binary version of an assembly-language program into the home-built CPU’s flash memory.

👁 Screenshot from RISC relay CPU site (via Homebrew Computing Web-ring)

The data is only 4 bits wide — but it was enough to create an impressive video showing the contraption calculating Fibonacci numbers up to 89. (After which the program starts the calculations all over again.)

While that project is based in the Netherlands, in true webring fashion, it links to other projects far away — including the site of David Brooks, the founder of the Homebrew CPUs WebRing. Brooks’ own site in Australia lovingly describes “the all-TTL machine I built in 1976” — taking visitors even further back into history.

“It all began in 1968, when I was at University in Bangor, N. Wales… Students punched their own programs (usually in Algol) on cards or five-track paper tape, and submitted them to the operators. This whetted my appetite for computing. When I left University, I lost access to a computer, and gradually developed the idea of building my own….”

More than half a century ago, the parts for a homebrewed computer were hard to come by, but undaunted, Brooks assembled “some wrecked hardware from the early 1960’s” including logic boards from an old IBM mainframe, later augmented with logic modules found in London surplus stores.

Ultimately an input-out mechanism was added — “a World War II surplus teletype machine,” and later a homemade case was proudly fitted around the finished unit.

And of course, Brooks’ page links to another homebrewed computer’s site — this one in France, sharing details of a home-built CPU crafted with field-programmable gate arrays.

Creating Magic

The website of retired software engineer Bill Buzbee describes a homebrewed computer built from 200 TTL chips — all of them carefully connected with thousands of individually wrapped wires.

“My wife and kids may not be impressed by my instruction set design, but all those wires ought to at least get some sort of reaction from them,” the site explains.

Just south of San Francisco, at his home in Half Moon Bay, Buzbee’s multiyear effort grew into its own monument to the tinkerer spirit, sometime around 2004. After installing the Minix 2 operating system, Buzbee could run hundreds of programs on his homebuilt computer — while even supporting multiple users and multitasking.

It now doubles as a webserver — and at one time was also a telnet server, hosting classic Unix shell games like Adventure, Eliza, Conway’s Game of Life, and Hunt the Wumpus.

The name Buzbee gave to his creation? Magic-1.

Soon this brought Buzbee a community of fans. Thousands of people have telnetted into Magic-1. Between 2004 and the summer of 2007 alone, they left 1388 guestbook messages.”

From around the world, they came — from Austria and New Zealand and Lafayette, Louisiana, all taking a moment of inspiration from Buzbee’s own quest to learn.

“At the end of the day, I wanted a working, and useful, machine that I understood completely,” Buzbee wrote on the site.

“Oh, and it had to have a real front panel with lots and lots of cool blinky lights.”

It’s the ultimate hobbyist project, with Buzbee putting in “the odd hour here and there” while pursuing his own career as a software engineer.

What kind of person builds their own computer? With a master’s degree in computer science, Buzbee’s been everything from a senior software engineer at Transmeta to a senior research scientist at Hewlett Packard Labs.

In 2008 Buzbee became a staff software engineer at Google, helping the Android team develop the Dalvik JIT compiler, and in 2018 he became a software engineer at Facebook.

But this hobbyist project seems just as meaningful. At the end of a biographical webpage, Buzbee marvels that his homebrewed computer “has gotten vastly more attention than I’ve ever imagined a silly nerd hobby project could get.

“It also enabled me to finally impress the teenage daughter. Not for doing my own computer, but for getting a magazine article about me,” he wrote, referring to how he was the “featured geek” in the summer 2005 issue of ExtremeTech Magazine.

Follow the webring’s links, and the stories keep coming, page after page, each one offering the near-magical tale of a determined hobbyist who summoned up their own hardware just by tapping their own reserves of ingenuity.

The webring is open “to any computer project featuring a home-built CPU,” explains the site’s official charter. That can be a field-programmable gate array (or FPGA), or a chip using transistor-transistor logic (TTL) — as long as it’s not a store-bought, off-the-shelf CPU.

And the webring’s official charter ends by sardonically asking if anyone will ever contribute a design that was built with vacuum tubes.