http://archive.computerhistory.org/resources/access/text/2012/06/102746190-05-01-acc.pdf
Wilson: So that was 1981. We converted a lot of the system range capabilities to make the BBC
machine [the BBC Micro] in the first place, and we built a lot of peripherals specifically for the BBC machine. And then we
started implementing language processors. So the BBC machine had a socket underneath of it for the
second processor, and its two-processor model. I designed the Tube, interconnection between the two
things, and wrote all the software protocols that ran the Tube. The Tube was basically a dual-direction
DMA controller plus four FIFO channels of communication so that you could virtualize your operating
system. So a second processor operating system, all they had to do was send the right commands
across the Tube, and the I/O processor machine would do all the right stuff for them. So we got all of that