Virtual memory allows you to use more memory than your machine has. If
something is transparent, it's there, but you can't see it; if something is
virtual, you can see it, but it isn't there. Virtual memory is implemented
by paging, in which only the parts (called pages) of programs actually used
are brought into memory. When the memory required by a program exceeds the
physical memory of the machine, unused pages are swapped out to disk.