[MC] Memory compactification is a solution to the external fragmentation problem.

Memory compactification involves moving data to combine several small unused parts of memory into a single larger piece of memory.

Memory compactification is not necessary with virtual memory, since consecutive pages of a process's virtual memory space are not required to reside in consecutive pages of physical memory. Compactification is only necessary in systems that do not use virtual memory.

External fragmentation cannot occur with virtual memory, but internal fragmentation can to a small extent. A given page might not be entirely in use. But the page is either entirely in memory or not. It is not possible to put just part of a page into the memory.