MacOS – Memory terminology in Mavericks Activity Monitory

activity-monitormacosmemory

In Mavericks, the Activity Monitor has changed its memory terminology. The columns available when viewing processes in the memory tab now include "Memory", "Real Memory", "Real Private Memory", "Real Shared Memory" and "Purgeable Memory".

I would have thought that since "Virtual Memory" has disappeared and "Memory" has appeared that they are equivalent, however that doesn't seem to add up because shouldn't then "Memory" be always greater than or equal to "Real Memory"? (If I'm interpreting the terminology correctly, Real Memory is the number of pages currently resident in RAM, and Virtual memory is the number of pages total, including those swapped out to disk, compressed, etc….) However in Activity monitor, "Memory" is always less than "Real Memory". Can anyone explain what this mysterious "Memory" metric is?

Best Answer

For each process there is

  • Real Memory (always at least as big as Memory)
    • Total Memory currently consumed by an application (including Virtual pages)
  • Memory
    • Memory used in RAM
  • Purgeable Memory
    • Memory which can be cleaned by MMU, if another process needs more real memory.

Then, for the system in total

  • Physical Memory
    • The amount of RAM installed.
  • Memory Used
    • The amount of RAM being used and not immediately available.
  • Virtual Memory
    • The amount of disk or flash drive space being used as virtual memory.
  • Swap Used
    • The space on your drive being used to swap unused files to and from RAM.
  • App Memory
    • The amount of space being used by apps.
  • Wired Memory
    • Memory that can’t be cached to disk, so it must stay in RAM. This memory can’t be borrowed by other apps.
  • Compressed
    • The amount of memory in RAM that is compressed.
  • File Cache
    • The space being used to temporarily store files that are not currently being used.
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