Trying to understand Mac memory management

Discussion in 'macOS' started by Dirtyharry50, Jun 24, 2012.

  1. Dirtyharry50 macrumors 68000


    May 17, 2012
    I am a very happy new iMac owner, recently having seen the light!

    I have a question about how OS X manages memory use.

    I had a bunch of apps open, including Parallels running a Windows XP VM. I just closed everything so only Activity Monitor is running on my desktop at the moment and the Firefox browser I am using to post here.

    Under System Memory, Activity Monitor reports 6.18 gigs is still in use. I know that normally when I start up this Mac, a little under 2 gigs would be in use before running any apps. So I am guessing OS X is caching code to improve performance by reducing hard disk reads? Is that right?

    What do these classifications for memory labeled by Activity Monitor mean? Here are the three names I do not understand along with the current values that total up to used ram of 6.18 gigs:

    Wired: 1.68 GB
    Active: 1.28 GB
    Inactive: 3.23 GB
    Total Used: 6.19 GB

    What the heck are "Wired" and "Inactive" ram that count as used? I am guessing "Active" is ram in use right now by the OS, this browser I am running and Activity Monitor? And I've wondered if "Inactive" ram was cache maybe? But Wired has me completely mystified.

    Could somebody clear up for me what these labels mean and perhaps give just a basic review of OS X memory management? Thanks a lot!
  2. GGJstudios macrumors Westmere


    May 16, 2008
    This may help:

    Mac OS X: Reading system memory usage in Activity Monitor
  3. Intell macrumors P6


    Jan 24, 2010
    Wired memory is memory that is used by the kernel and for the most part cannot be put into swap or released. Active memory is memory that is in use and can be swapped or released if needed. Inactive memory is what remains of a program when you close it. If the app that you closed is reopened, its memory goes from inactive to active. This speeds up launch times and general computing. If the system is low on free memory, it will purge the ram of the oldest inactive contents to free up memory. Remember, Mac OS X is a UNIX based operating system and like most UNIX systems, free ram is wasted ram.
  4. Dirtyharry50 thread starter macrumors 68000


    May 17, 2012
    Wow! Such fast and helpful replies! Thank you both.

    I did go read the linked article. Thank you for pointing that out. This all makes perfect sense to me now.

    Thanks again guys!

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