The BBC Micro wraparound is designed in rather than being apparently some kind of unreliable poorly-defined accident. There's a specific bit of hardware that su

The BBC Micro wraparound is designed in rather than being apparently some kind of unreliable poorly-defined accident. There's a specific bit of hardware that subtracts a specific amount if the address runs off the top of RAM, so the video memory (typically the top 10 KB or 20 KB of RAM) is effectively circular. For single-buffered infinite scrolling, this is exactly what you want, and this is how the BBC Micro's 640 pixel wide bitmap mode scrolls nice and quickly (something you'd never manage otherwise with a 2 MHz CPU), and why there are a fair number of infinite 4-way scrolling games on the platform. It's a shame more platforms didn't have this kind of thing designed in.