What's the difference between free and inactive memory?

Question

What's the difference between free and inactive memory?

I have noticed that via iStatPro I have been reaching the point where I only have around 50mb of free RAM at times, but I have about 450mb of inactive RAM. I'm just wanting to know what the difference is, I'm thinking about putting 4GB in my iMac but I don't want to unless I need it. So yeah can someone explain the differences?

[img] http://img513.imageshack.us/img513/124/screenshot20091102at194.png[/img]

Macbook, Mac OS X (10.5.6), White Macbook, 2.0Ghz, 2GB RAM, Nvidia 9400m, 320GB 7200RPM HDD

Posted on Nov 2, 2009 11:44 AM

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Answer 1

varjak paw

Level 10

170,200 points

Nov 2, 2009 12:09 PM in response to Community User

Take a read through this document:

http://www.thexlab.com/faqs/lackofram.html

It will help you determine if more RAM will help your system.

Regards.

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Answer 2

Dave Stowe

Level 5

5,180 points

Nov 2, 2009 12:11 PM in response to Community User

This link is to reading memory usage using Apples 'Activity Monitor'....

http://support.apple.com/kb/HT1342

you can also Google your question for more detailed info

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Answer 3

Nov 2, 2009 12:34 PM in response to Community User

Four types of memory appear in the System-Memory pie chart when using Activity Monitor: Wired, Active, Inactive, and Free. "Used" is the total of the first three. The total of the four is the amount of RAM installed. RAM is the high-speed memory used to store information that is in use or was used most recently. "VM (virtual memory) size" is the amount of disk space currently reserved for paging information into RAM and caching information to disk as becomes necessary because of demands on RAM. OX X can "virtually" use more memory than the amount of RAM installed.

Wired memory contains information that can't be cached to disk—i.e., it must stay in RAM. The amount of wired memory depends on what applications one is using. Active memory contains the information that currently is in RAM and is actively being used. Inactive memory contains information that is no longer being used and that has been cached to disk.

You don't appear to need more RAM. [Here is a read (the second email)|http://www.macosxhints.com/article.php?story=20010613140025184] that will help you understand your situation better. Indicators of a need for memory are perceived slowness, the rate at which pageouts occur, and the total size of one's swapfiles.

Message was edited by: donv (The Ghost)

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Answer 4

Nov 2, 2009 12:42 PM in response to donv_the_ghost

Thanks for the info everyone, I've just read through it all.

Am I right in thinking then as long as I have a decent amount of inactive RAM in my system there is no need to add more? If I get to the point where I have a very low amount of inactive and free RAM then I should consider putting more in?

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Answer 5

BobHarris

Level 9

53,147 points

Nov 2, 2009 12:50 PM in response to Community User

Personally, I like to monitor pageout activity using the Applicaitons -> Utilities -> Terminal command:


sar -g 60 100

and if the output shows mostly zeros every 60 seconds, then I most likely do not need memory.

If I have sustained high pageout rates every minute, or if I have pageout spikes when my performance is really bad, then more memory would be beneficial.

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Answer 6

Kappy

Level 10

361,741 points

Nov 2, 2009 12:54 PM in response to Community User

I don't wish to confuse the issue but you might like to review the following:

About OS X Memory Management and Usage

Reading system memory usage in Activity Monitor
Memory Management in Mac OS X
Performance Guidelines- Memory Management in Mac OS X
A detailed look at memory usage in OS X

Understanding top output in the Terminal

The amount of available RAM for applications is the sum of Free RAM and Inactive RAM. This will change as applications are opened and closed or change from active to inactive status. The Swap figure represents an estimate of the total amount of swap space required for VM if used, but does not necessarily indicate the actual size of the existing swap file. If you are really in need of more RAM that would be indicated by how frequently the system uses VM. If you open the Terminal and run the top command at the prompt you will find information reported on Pageins () and Pageouts (). Pageouts () is the important figure. If the value in the parentheses is 0 (zero) then OS X is not making instantaneous use of VM which means you have adequate physical RAM for the system with the applications you have loaded. If the figure in parentheses is running positive and your hard drive is constantly being used (thrashing) then you need more physical RAM.

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