Hardware - Resident Memory
1 - About
Resident memory is the physical memory actually in operational use by a process. Over time, the operating system may swap out some of a process's resident memory according to a least-recently-used algorithm to make room for other code or data. Thus, a process's resident memory size may fluctuate independently of its virtual memory size.
In a properly-sized OS, there is enough physical memory, so that swapping is disabled and should not be observed.