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Memory

OS X has very efficient memory management. It will automatically allocate memory and adjust the contents of memory as needed.

Info on the memory:

Memory: This is the total amount of RAM installed.

Used: This is the total amount of RAM used.

Wired: Information in RAM that can't be moved to the Mac's drive. The amount of Wired memory depends on the applications you are using.

Active: This information is in RAM and has been recently used.

Inactive: This information is in RAM but it is not actively being used; it was recently used.
For example, if you've been using Mail and then quit it, the RAM that Mail was using is marked as Inactive memory. Inactive memory is available for use by another application, just like Free memory. However, if you open Mail before its Inactive memory is used by a different application, Mail will open quicker because its Inactive memory is converted to Active memory, instead of loading it from the slower drive.

You can use the Purge button to remove the information in the inactive memory.
Note: While purging the inactive memory, the Finder may slow down and not respond for several seconds.

Info on the virtual memory swapping:

Number of Swap files: Number of files that's being used for virtual memory.

Total Size: This is the total size of the files used for virtual memory.

Used: This is the amount of information copied to the swap file on the drive.

Free: This is the size available of virtual memory.

Page ins:/Page outs: This refers to the amount of information moved between RAM and the Mac's drive. This number is a cumulative amount of data that OS X has moved between RAM and the drive.
Tip: Page outs occur when the Mac has to write information from RAM to the hard drive (because RAM is full). Adding more RAM may reduce page outs.

You can choose to turn off the virtual memory.
Note: If you have less than 4 GB memory installed, it's not recommended to disable virtual memory swapping, because the applications could crash.