How is VIRT different from RES?

VIRT (Virtual Memory Size) and RES (Resident Set Size) are both metrics used in process monitoring tools like htop and top, but they represent different aspects of memory usage:

1. VIRT (Virtual Memory Size):

   • Represents the total amount of virtual memory allocated for a process.
   • Includes all types of memory, such as:
     • Physical memory (RAM)
     • Swap space
     • Shared libraries
     • Memory-mapped files
   • It reflects the total addressable memory space that the process can use, regardless of whether it is currently in physical RAM or on disk.

2. RES (Resident Set Size):

   • Represents the portion of a process's memory that is currently held in physical RAM.
   • It indicates the actual memory being used by the process at that moment.
   • RES does not include memory that has been swapped out to disk or memory that is allocated but not currently in use.

Summary:

• VIRT shows the total virtual memory allocated (including swapped and shared memory), while RES shows the actual physical memory currently in use by the process. Understanding both metrics helps in analyzing memory usage and performance of processes.