Some games were so hard up for memory that: - they used the port-direction bits in the parallel I/O chip registers as temporaries. After all, you only care abo

Some games were so hard up for memory that: - they used the port-direction bits in the parallel I/O chip registers as temporaries. After all, you only care about user input for a tiny part of the video frame - some games didn't use the stack . . . or not all the time. So the stack pointer was just another register, too