Have you ever wondered what all that system memory stuff in the Activity Monitor was all about? Understanding the terminology – free, wired, active, and inactive RAM – can help you decide if your Mac has enough memory.
A vocabulary overview
When a Mac’s system memory is being used, OS X doesn’t just lump it all together. It’s very neatly organized, as you will soon find out. One thing to mention beforehand, though, is that information stored in RAM sometimes gets temporarily moved to and from the hard drive when there isn’t enough RAM available. Of course, this slows a Mac down considerably, so it generally only occurs as a last resort when the system runs out of RAM.
Free memory
As one might expect, this is the RAM that is sitting there with nothing to do. It is completely free for the system to use when needed.
As one might expect, this is the RAM that is sitting there with nothing to do. It is completely free for the system to use when needed.
Wired memory
Critical information stored in RAM by the system, its kernel, and some key application components. This stuff is basically frozen – it allocates its space and never moves to the hard drive or gets replaced with user-level data when RAM becomes scarce. An interesting thing to note about wired memory is that it scales based on how much total system memory is installed. For example, a Mac with 1GB of RAM may show 400MB of wired memory, while a Mac with 4GB of RAM may use 700MB. The more memory you have, the more your Mac wants to use it!
Critical information stored in RAM by the system, its kernel, and some key application components. This stuff is basically frozen – it allocates its space and never moves to the hard drive or gets replaced with user-level data when RAM becomes scarce. An interesting thing to note about wired memory is that it scales based on how much total system memory is installed. For example, a Mac with 1GB of RAM may show 400MB of wired memory, while a Mac with 4GB of RAM may use 700MB. The more memory you have, the more your Mac wants to use it!
Active memory
Information currently in use or very recently used. If you’ve got Safari, GarageBand, iTunes, and Photoshop all going at the same time, your active memory is likely fairly high. Quit one or two of these applications and active memory will shrink. But not all of it will go straight back to free memory. This is because some goes to the Inactive Memory.
Information currently in use or very recently used. If you’ve got Safari, GarageBand, iTunes, and Photoshop all going at the same time, your active memory is likely fairly high. Quit one or two of these applications and active memory will shrink. But not all of it will go straight back to free memory. This is because some goes to the Inactive Memory.
Inactive memory
One of the great things about Mac OS X’s memory management system is that it never stops working for you. Inactive memory is basically a handy storage space for convenient access to your most used tools. Let’s say you were working in iPhoto and decide to quit it. Some of the information that was stored in active memory by this application will be moved to inactive memory. This way, when you open iPhoto next time it will load up faster than before. Why? Because the computer is not reading everything from its slow hard drive again.
One of the great things about Mac OS X’s memory management system is that it never stops working for you. Inactive memory is basically a handy storage space for convenient access to your most used tools. Let’s say you were working in iPhoto and decide to quit it. Some of the information that was stored in active memory by this application will be moved to inactive memory. This way, when you open iPhoto next time it will load up faster than before. Why? Because the computer is not reading everything from its slow hard drive again.
Page ins
The amount of information moved from the hard drive to RAM since the last system startup. Every time you open an application or file, this number goes up.
The amount of information moved from the hard drive to RAM since the last system startup. Every time you open an application or file, this number goes up.
Page outs
The amount of information moved from RAM to the hard drive since the last system startup. When RAM is running low or needs to be shuffled around to the hard drive to accommodate higher priority data, this number increases.
The amount of information moved from RAM to the hard drive since the last system startup. When RAM is running low or needs to be shuffled around to the hard drive to accommodate higher priority data, this number increases.
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