It's an excellent piece of work, and you could probably use similar techniques to create addons for other 8-bit systems, but overall it's probably not super-int

It's an excellent piece of work, and you could probably use similar techniques to create addons for other 8-bit systems, but overall it's probably not super-interesting for non-BBC Micro fans ;) BBC games tend not to work with a coprocessor - but a lot of business/serious software probably would (not much use these days of course...), and you can always use it for programming. I've got a 16MHz 6502 coprocessor for my BBC and it works well. The coprocessor system is quite well designed, so the coprocessor has basically nothing to do but run BASIC or whatever, and the main 2MHz CPU only gets used for I/O. I/O-heavy stuff can be a little bit quicker sometimes; calculations and stuff run about as much more quickly as you'd expect from the clock rate. (In fact, they're a little bit quicker than that - because the coprocessor doesn't have to handle I/O, timers, keyboard scanning, etc., all of which can bog down the main CPU a little.)