Understanding Memory Pressure in OS X Mavericks

If you haven’t upgraded to OS X Mavericks yet, you should for a whole host of reasons. One of these reasons is the new Memory tab in Activity Monitor. It’s gotten a huge upgrade and it makes understanding memory usage in OS X a lot easier than previous versions.

Using the new revamped memory statistics, you can forget about the confusing Free, Wired, Active, Inactive and Used values. Those values were probably the most confusing features of OS X. 99% of the people who I know that own a Mac had no clue what any of it meant.

If you recall, the memory tab in previous versions was called System Memory and looked something like this:

old activity monitor

These statistics were overkill for most users and one of the reasons why people call Macs less user-friendly. Thankfully, OS X Mavericks fixes all of this by letting you focus on one statistic: memory pressure. Here’s what the new Memory tab in Activity Monitor looks like:

memory pressure

The Memory Pressure graph is in the middle of the two statistics sections. Again, there are statistics here that could confuse people like App Memory, File Cache, Wired Memory, but you really don’t have to worry about that anymore. Now you can just look at memory pressure and as long as it’s green, you are good to go.

On the left hand side are the main memory statistics: total memory (physical memory), memory used, virtual memory and swap used. Physical Memory is the total RAM you have installed on the system. Memory Used is the total memory that is currently in use, not necessarily by app, but everything.

The “everything” I am referring to are the four items on the right. Basically, you can add up the four items on the right and you should end up getting very close to the Memory Used value. Let me explain these values:

App Memory – The amount of memory being used up by programs.

File Cache – Memory that is available in RAM to be used by apps that contains recently used files. For example, if you close Safari, then the RAM that Safari was using will be marked as File Cache and can be used by another app. However, if you don’t open another app and you open Safari again before that memory gets overwritten, Safari will open faster because it’s file cache still exists.

Wired Memory – This is memory that can’t be moved to disk and therefore must remain in the physical RAM. It also can’t be used by other apps.

Compressed – Memory in RAM that is currently compressed, so that there is more memory available to other apps. Compressed memory is a new feature in OS X Mavericks.

Virtual Memory is the amount of memory that the apps have asked for and does not indicate the amount of memory actually being consumed. Swap Used means data is being transferred to and from your hard disk and RAM. It’s ok if this value is small (<100 MB) and it will never be 0, but a high value indicates a memory problem.

Now let’s talk about memory pressure again. If you see a lot of amber or red bars in the graph, you are having memory issues that will be slowing down your computer.

memory pressure

Amber or yellow means that memory resources are getting low. Red means you’re almost out of memory or it’s completely full. Of course to solve the actual problem, you really only have two choices: either close apps that are eating up large amounts of memory or upgrade your RAM.

It should be noted that there are times when Memory Used will be very close to your Physical Memory value, but this does not mean your system doesn’t have enough memory. Instead that memory might be used by the File Cache, which can be quite large. As long as memory pressure is green, don’t worry if it looks like all your memory is being “used”.

Again, this is a pretty big overhaul of memory management in OS X and not only does it make your Mac run more efficiently, it’s also a lot easier to understand. If you have any questions, let us know in the comments. Enjoy!

Comments [7]

  1. Thanks for this helpful article.

    I note, FYI, that “swap used” on my MacBook Pro says “0 bytes,” so there mus be some conditions in which this is true. Only OS X, finder & TextExpander running…

  2. Thanks for the information guys. How much RAM is in your systems? I tried my best with 8 GB and it never went to 0 for Swap Used. On Apple\’s site, they also mention that there always might be a little swap used, but that doesn\’t mean you are running out of RAM, so I assumed it could never go to zero. Good to know that\’s no true.

    1. @George – No, you have no memory problem at all! Those are great numbers and the green bar is so low, meaning not very much memory is being used.

  3. A very good article, Easy to understand and very “user friendly” I mean its excellent. My Swap shows 0 bytes and why I started looking for an understanding of Memory on Mac? The answer is at the bottom of the article, I thought I’m using all my ram Because my “Memory Used” is 3.97GB and my “Physical Memory” is 4GB on my MacBook Air so I thought I’m using all of it. I was like wtf.. lol But Thank you very very much. A++

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