this is a conceptual question that came up from an issue I have.

I've been monitoring memory usage with iStat Pro and Activity Monitor for some weeks, since my MacBook Pro (OSX 10.8.4 Mountain Lion 8Gb RAM) became slower to change between applications and started to take some seconds to show me text when I start typing, or even take more than 5 seconds to let me put password when reopening my (turned on) laptop.

I've been reading some topics about this, and generally when I close Safari and Chrome and reopen them, it gets better, although sometimes I need to purge on Terminal to free up some memory, but actually I don't have a good idea about the way OSX manages its memory.

As far as I understand, Active Memory is for tasks that are currently being executed, Inactive Memory is for closed apps that may be potentially reopened, Free Memory is fully available memory, but what about Wired Memory, Swap Memory, VM size and Page ins / outs I see on Activity Monitor?

Since OSX comes pre-configured to have optimal performance (theoretically), I don't really like to purge and I don't want to change memory swapping configurations before having a good understand about what I am doing.

Can anyone better explain to me how these memories works out and make some suggestion for my issues? Specially the one with the password, If it helps, I noticed it became tougher when I started to use WiFi connection and turned WiFi permanently on.

EDIT: After OS X 10.9 Mavericks, the password issue has disappeared either on WiFi or not. Now I can open the laptop and immediately start typing my password and it accepts.

  • That edit should be a new question
    – mmmmmm
    Commented Oct 27, 2013 at 13:18
  • possible duplicate of Isn't Inactive memory a waste of resources?
    – mmmmmm
    Commented Oct 27, 2013 at 13:19
  • You should never have to run commands such as purge. The operating system has much more information than you do about memory usage and processes and knows how to handle memory handling and swapping better than the user.
    – Bert
    Commented Oct 27, 2013 at 13:53

1 Answer 1


Wired memory is memory that the Operating System has reserved for itself, and it cannot be written to disk.

VM Memory is the amount of space on your disk that the system has allocated for virtual memory. This is slow, and one of the main reasons why running low of free RAM will bring your system to a crawl.

Page ins / outs are when RAM memory is written to the disk (out) and when it is copied back from the disk into RAM (in).

Swap is how much of the VM Memory the system is actually using.

This, and more, can also be found here: http://www.interrupt19.com/2009/06/15/os-x-memory-usage-explained/ and here: http://support.apple.com/kb/HT1342?viewlocale=en_US&locale=en_US

Make sure you have enough free space on your disk for the OS to swap as needed. A good rule of thumb is that 10% of your total disk capacity should always be free. Furthermore, have you noticed any particular apps giving you trouble? Those tools you're using can be powerful for narrowing down what is causing your problem. Also, if you are running Chrome and Safari simultaneously, I suggest you only run them one at a time, as they both tend to be memory-hungry in my experience.

  • thank you for your time. No particular apps, just the WiFi stuff when logging in. I recognize Chrome+Safari is memory expensive, but anyway I boosted memory from 4 to 8 Gb when I bought it because I knew I tend to open lots of tabs, even using read it later stuff... What shucks is that Safari is well synced with my Apple stuff, and Chrome with my Google stuff, and that's why I use both, we can't use multiple services anymore in peace...
    – rafa
    Commented Jul 15, 2013 at 11:57
  • This is a minor point, but is your RAM composed of 2x4GB sticks, or 1x8GB stick? I believe having two equal sticks is slightly faster than having one stick. In any case, do things improve if you keep WiFi off?
    – Tortilla
    Commented Jul 15, 2013 at 20:59
  • 2x4GB and indeed Apple says its better like that. Turned off WiFi, I still have the slow login problem, maybe it was just a coincidence, but anyway, 2 friends of mine reported the same problem with slow login... could it be just an issue from after some system update? I also updated Xcode recently (though it's often completely closed). Anyway it was already very helpful your explanation about the memory stuff
    – rafa
    Commented Jul 16, 2013 at 23:03
  • It may just be a characteristic of the OS version you all are running. To be honest, I have the same problems you have pretty frequently, but I have so much stuff on my computer I assume it's a natural consequence and have come to live with it. I'm sorry I can't be of more help.
    – Tortilla
    Commented Jul 17, 2013 at 2:47
  • "VM Memory is the amount of space on your disk that the system has allocated for virtual memory" No, it is not. The VM is the address_space the OS uses. As the name says, it is virtual. You confuse it with swap which is indeed on the disk: that is used by the OS if the RAM gets nearly full. And yes, that is slow. Commented Oct 21, 2014 at 6:21

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