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I see that the Activity Monitory shows a variety of information about System Memory usage. Are their particular values or perhaps ratios that would indicate with certainty that I need to upgrade my RAM?

At this moment, I'm running more than I usually do. I've got a couple of virtual machines running, several resource intensive development tools, three different browsers (Chrome, Firefox, and Safari), Mail, a database application, and a productivity tracking application. Normally, I run about half of those simultaneously. I have 4GB of RAM installed, and the Activity Monitor reports that I have:

Free: 518.5 MB
Wired: 1.08 GB
Active: 1.84 GB
Inactive: 587 MB
Used: 3.49 GB
VM size: 155.62 GB
Page ins: 1.08 GB
Page outs: 792 KB
Swap used: 16.7 MB

I know it is "only" about $90 to upgrade, but I see no point in spending money unless I truly acquire new capabilities or a notable increase in performance.

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In case you didn't already know, you can buy RAM from Crucial at much lower prices than what Apple charge. However, this only applies if you're comfortable with replacing the ram yourself. – Jasarien May 26 '11 at 11:22
Adding RAM to a unibody Macbook Pro yourself is not the easiest thing to do.. – Joseph May 26 '11 at 11:28
Sure it is. A few little screws on the base and that's it. It's not as easy as multipart cases, but it's hardly an epic task. – Lukasa May 26 '11 at 13:35
If you already have 4GB, then ensure your MacBook Pro model and OSX version support more than 4GB before spending any money on it. :) MacTracker may help you figure that out. – Ƭᴇcʜιᴇ007 May 26 '11 at 15:39
If you find any answer satisfying please consider accepting it. – vbence Jun 7 '11 at 9:40
up vote 2 down vote accepted

When you open up the Activity Monitor and check the System Memory tab (image examples here or here), you can see a label next ot the cake saying Swap Used. This means that much physical memory were used if it were available. Now the disk is used instead (which is way slower).

Check this when you opened up Photosop, Safari, Xcode (if you are a web developer) or the programs you usally use during your work. Now check the number.

If you have less then 8 gigabytes of ram, then performance can be improved if you use any of todays programs. (They get hungrier every day).


Your numbers show a low swap utilisation. The real question is whether your (more than usually) open programs run smooth and if the performance was satisfactory. If you have more RAM it will be used at least for caching. And you can have more memory for your VMs too.

If you are satsfied then upgrade is not neccessary at the moment. - But in the long run don't wait until your HW is no longer suuported and no memory modules are available for it.

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It depends how much RAM you have to start with.

Upgrading from 2Gib to 4Gib makes a world of difference because you can have a lot more apps open at the same time.

However, upgrading from something like 8Gib to 16Gib is not going to make a whole lot of difference unless you run Photoshop, a video editor, and a whole bunch of other apps at the same time.

Upgrading your RAM is one of the cheapest ways to get a performance boost from a middle-aged system.

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From command line you can use vm_stat. Pageouts and Pageins are the most interesting statistic. It tells you how often you had to write/load a page to/from swap. Ideally with enough RAM it should be zero.

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So the Pageouts/ins are historical values, and the swap is a current value? Ideally, all would be zero or just swap? – Michael Prescott May 26 '11 at 15:28
@Michael: Total since boot. If you run it with interval option it's total since boot in first line, change since previous in each consecutive line. – vartec May 26 '11 at 16:20

In my opinion OS X tends to use RAM more than Windows would do.

Example: I have a Macbook Pro with 8GB of RAM. Doing normal browsing stuff and having a few applications open, 5.47 are shown as used. On my old Macbook Pro, I had 2GB RAM, so you would think I couldn't even run the OS, but still it worked perfectly with exactly the same applications running.

Having more space available means that the OS can "leave" more applications in a state that allows them to resume faster and having to write less data to the hard disk.

So, if you have a "normal" (non-SSD) hard disk, you are most probably going to notice increased performance, especially when you switch application context a lot – or like to keep many applications open at the same time.

If you want to run RAM-hungry applications like video or audio editing, then the change will be even more drastic.

Those are very general statements, but as you didn't mention your specific needs, your hardware configuration or what you wanted to buy exactly, I can only say that upgrading RAM will definitely increase performance and $90 are most certainly worth it.

How much it increases depends on your initial configuration and software needs though.

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Not on a Mac right now to double-check, but isn't pages in/out in Activity Monitor a useful tool here? Non-zero values mean we swap, very large values mean we swap too much, something like that? – Daniel Beck May 26 '11 at 11:31
Yes, one could check that, I wasn't trying to be any more specific. Not on a Mac either, but the System Memory tab has "Page ins and Page outs" and an indication of how much Swap is used at the moment, I suppose. @Michael Prescott Those would be an indicator of how much your hard disk is involved due to lack of RAM space. – slhck May 26 '11 at 11:34

Windows has a feature called "Windows User Experience" that tells you the "experience score" of each component of your machine - RAM, graphics, processor, etc. This is a great feature and you should create the same picture mentally.

You should just bear in mind that upgrading the "lowest common denominator" will be best.

Upgrading from 2 GB RAM to 4 GB is a good upgrade, but anything more than 4 will do nothing on a 32-bit processor. If you have the weakest processor, it will also be worthless. Bear things like this in mind. Compare with the rest of your specs.

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This is about OS X, and since it's a different OS the numbers provided by Windows might not be useful. – Daniel Beck May 26 '11 at 11:32

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