Meet the Megaprocessor: a 16-bit CPU the size of a room

Chipmaking is a relentless competition to make transistors smaller and smaller. Such refined technology is as inscrutable to users as angels dancing on the head of a few hundred copper pins, so James Newman set out to make a working CPU whose every connection can be explored and understood by students.

"Like all modern processors the Megaprocessor is built from transistors," he writes. "It's just that instead of using teeny-weeny ones integrated on a silicon chip it uses discrete individual ones... Thousands of them. And loads of LEDs."

The resulting machine took two years to construct and recalls the earliest room-filling electronic computers, with banks of blinking lights and ropes of cable linking each refridgerator-sized peripheral. But this time, it's by choice rather than limitation: with a light on every connection, you can see the logic and movement of data through the chip in person.

Ten meters wide and 2 meters tall, the 16-bit Megaprocessor is deliberately simple and slow. Clocked at 20kHz, it could feel at home in an airport-sized Commodore Amiga or classic Mac, though it's not quite as complicated as the Motorola 68000 that inspired it.

There's already software to play with, though, including a rough implementation of Tetris. You can download an emulator to get started on making your own.

"I didn't plan on ending up here. I started by wanting to learn about transistors," Newman writes. "Things got out of hand.