Now, why might a ten-cart accessory have 21 buttons???
(BTW, the BBC Micro as equipped with a Raspberry-Pi based second processor can now run a PDP-11 model, and there is a BBC Basic port to this model. There could, possibly, be a unixy world in there, if it could conform to the API that the Beeb offers. Which is to say, I’m sure it could be done, but I believe it to be non-trivial, and probably would be low performance.)
Regarding ARM-enhanced BBC Micros, it’s much the same with the Atari 2600: there are cartridges which run an ARM processor and an obscene amount of memory by bank switching. In essence, the Atari 2600 is then just a quirky terminal.
BTW, the Spectravision CompuMate was real and it ran BASIC!
(For the nasty details: The problem with any Atari 2600 enhancements is that the cartridge port does not include an address write signal. Therefore, you have to come up with a convention were selecting a particular address (for read or write) substitutes the wirite signal for the next address select. This is usually used for bank switching. However, there were contemporary enhanced cartridges with a processor, either for sound or for churning out a byte stream at a particular address to achieve some graphics that wouldn’t have been possible when having to loop over these bytes in a conventional way. Pitfall II is an example for this. Running BASIC from the CompuMate was quite an achievement.)
