Óscar Toledo G.'s Open-Hardware ISA Expansion Card Puts an Inmos Transputer in Your Vintage PC

Developer, author, and vintage computing enthusiast Óscar Toledo G. has designed a modern expansion board to put an unusual piece of computing technology into more mainstream systems with an Industry Standard Architecture (ISA) slot: a transputer ISA board.

"I developed software for transputers in the years 1993-1996," Toledo explains. "A few months ago, I wrote some articles about my experiences, and most recently I developed a transputer emulator in JavaScript. After my transputer emulator in JavaScript was working, I got curious about running my software on a PC computer. I have several PC motherboards with ISA connectors, and I decided to build a card compatible with the Inmos B004 (a single board to test transputer processors). Out of curiosity, I decided for compatibility because I wanted to run the Inmos Occam compiler."

Few involved in technology today are ignorant of the evolution of mainstream microprocessors, starting with Intel's market-launching 4004 and leading to the high-performance many-core machines of today — but the transputer is less well known. Designed by Inmos in the 1980s, the transputer concept aimed to address what was seen as an upcoming performance bottleneck in traditional microprocessor design by delivering an architecture dedicated towards parallelism — a precursor to the multi-core, multi-thread mobile, desktop, and server processors today.

To build a modern transputer board — not a dedicated computer, but something closer to an accelerator card that serves as a coprocessor in a more traditional microcomputing system — Toledo picked up original Inmos T805 transputer boards, stick-like PCBs with a 30MHz transputer chip and a chunk of memory designed to be used as building blocks for a multi-processor transputer system.

"The TRAM board contains the transputer and its memory," Toledo explains of his design, initially built on prototyping board before being moved to a dedicated PCB designed in KiCad. "It is connected to the ISA board with a Inmos C011 chip that serializes and deserializes the communication link. This chip is accessed via the ports 0150H-0153H. My ISA board also provides a 5MHz oscillator, two flip-flops to reset and analyse the transputer, and a tri-state gate to read the error status."

After some tweaks — one to address a speed issue, which saw the 30MHz transputer chip limited to 20MHz, and another to fix an compiler fussy about a triggered error flag — Toledo had a working Transputer board, compatible with software he had originally written back in the 1990s. While the performance is, as you would expect, a mile away from a modern microprocessor, it's a slice of history nevertheless — and there's more to link modern many-core systems to Inmos' work than separates them, suggesting the technology's commercial failure was one more of timing than approach.

Toledo's full project write-up is available on his website; design files are available on GitHub under a BSD two-clause license. Toledo has also confirmed that he has "several" extra PCBs, available to order fully-built and tested for $74 delivered in the US — just add an Inmos TRAM board and C011 to be up and running.