When a program attempted to access values in memory that had been paged, the VM system would once again intervene, writing out some other page of memory and loading the requested one back in. This is invisible to the program, to it, it appears there is a single large memory and its data is always available. Programs written in a VM system are otherwise similar to those on earlier machines.
When a program tries to access memory that has been moved, the VM system intervenes by writing another page and reloading the requested one. This action is invisible to the program; it appears there is a single large memory space with always available data. Programs written for a VM system are otherwise similar to those on earlier machines.