1545 Views 6 Replies Latest reply: Nov 2, 2009 12:54 PM by Kappy
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)
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.
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.