The RSS indicates the non-swapped physical memory usage by the process and the VSZ stands for the Virtual memory used by the process. So I believe RSS indicates the exact RAM usage. The Virtual Memory is the combination of RAM & Disk space used (swap) by the process according to http://stackoverflow.com/questions/4970421/difference-between-virtual-memory-and-swap-spacehttps://stackoverflow.com/questions/4970421/difference-between-virtual-memory-and-swap-space