RAM and Activity Monitor

Discussion in 'Mac Pro' started by xBeeza, May 17, 2008.

  1. xBeeza macrumors newbie

    Apr 30, 2008
    A question for those that run Activity Monitor.

    I just installed an additional 8 gigs of OWC Ram in my 8 core 2.8 w/2gigs Ram. Everything is running smoothly although my system does seem to take longer to shut down. When I check "About this Mac" it shows up with the 10 gigs. I run Activity Monitor and the full 10 gigs shows up there as well. Initially it shows up on the "Free" column but after a couple of hours the balance of free ram moves to the "Inactive" column. I assume it's still available for use when need but I just wonder if this is what others experience. When I just had the original 2 gigs the free balance never moved to the Inactive column. Does anyone know the difference between Inactive and Free ?

  2. martinlk macrumors member


    Jun 20, 2005
    Aalborg, Denmark
    I think inactive memory is allocated memory that has been paged out to disk. Allocated memory becomes inactive after a while of not being used. When this happens it is paged to disk so that the OS can quickly deallocate it in case more free memory is needed. The reason that it becomes inactive and not free is that there'd be no reason for the OS to deallocate memory that could in fact be referenced by some running process again.
  3. Infrared macrumors 68000


    Mar 28, 2007
    Here's an analogy. In the analogy the book is the data, the
    shelves are long term storage, and the reading tables are RAM.

    People go to a library and there are several hundred tables
    there. It's bad form to read at the shelves, so they take their
    books to the tables to read. When they've read what they want
    to, they get up and go but they leave their books on the tables.

    Now, if someone else comes to the library and wants to read
    those same books, they don't have to get them off the shelves.
    Rather, they just sit down at the tables where the books were
    left before. This is good because it means less moving around of
    stuff in the library, and so less noise. And we all know how
    much librarians hate noise. If they had their way, ears would
    never have been invented.

    Anyway, let's continue. If someone wants to read a book and it's
    not already at a reading table, they need to get the book and
    find a free table. But suppose there are no free tables? Well,
    there may be some inactive tables, and these are tables that
    have books on them left by other people, but don't have people
    sitting at them. So the librarian clears a table for you,
    warns you sternly about making any noise, and you make your way
    to this newly freed table.

    And that is essentially what is happening with your RAM.

    (Eek! That's a bit wordier than I intended. )
  4. Coprolite macrumors member

    Aug 1, 2007
    Fort Worth, TX
    Good analogy, but...

    Given that it is loosely tied to a library, this makes good sense. Unfortunately, libraries don't have dynamic way to track their books inside the library. If it is on a reading table, no one would know where to find it until the shelf restocker puts it back. If we go high tech RFID, then we'd be golden......
  5. xBeeza thread starter macrumors newbie

    Apr 30, 2008
    Thanks for all of the replies. I understand the library analogy but does the ram move to Inactive because it was previously used by a process (someone taking a book off the shelf)?. The transfer of ram in the Free bucket to the Inactive bucket seems to happen when the system is idle for a period of time as opposed to me actually loading programs or files. Also it never happened with the any Free balance when I had only 2 gigs of Ram installed.

  6. martinlk macrumors member


    Jun 20, 2005
    Aalborg, Denmark
    Memory becomes "inactive" after not being accessed for a while. Imagine an app using a portion of memory frequently. Freeing this portion and allocating it to another process would be extremely unwise since whatever was freed would have to be allocated again somewhere else. If, however, the system keeps track of the portions of memory that have not been used recently, it can free these parts with there being a lower risk of having to page stuff back in again.

    Free memory will never become inactive. It's the other way around.

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