Acorn Communicator
Some familiar RISC OS commands don't work. PAGE and HIMEM are a lot higher than we would see on an 8 bit Acorn. In fact, this is because the Communicator introduces (or borrows, depending on which came first) the concept of multiple tasks running at the same time, each having its own space in RAM which doesn't get overwritten when one of the other tasks is doing something. Exiting BASIC and returning to the menu shows that the BASIC task is active, and returning to BASIC brings back exactly the same screen as before.