It was great when virtually everything was mapped 1:1 into "real" memory, even video memory. In those days, everything was a memory address, just like "everythi

It was great when virtually everything was mapped 1:1 into "real" memory, even video memory. In those days, everything was a memory address, just like "everything is a file". Then came the realization you could alter any memory location, and further, you could write a tiny TSR to do things...