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How to check what size memory modules are in your Mac

I was afraid that my article and video on “How to upgrade memory in your Mac” may have been a bit geeky, but I was overwhelmed by how many readers were interested in the topic. Some dove right in and bought more memory for their Mac.

Newsletter subscriber Dean wanted to upgrade his MacBook Pro and asked a great question about what size memory modules he should buy. I told him that first we had to find out what memory modules he already had. In this video I show how to quickly figure that out. I also discuss memory configuration options and some things you absolutely must get right when buying upgraded memory for your Mac.

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Checking your Mac’s memory configuration

The System Profiler application can show you many things about your Mac, including important details about the installed memory. An easy way to launch the System Profiler is to choose “About This Mac” from the Apple menu, and then click on the “More Info…”. In the Hardware category you’ll see a Memory section. It will display the size, type and speed for each memory module in your Mac.

Deciding what size memory modules to buy

When buying memory for your Mac, you have two basic constraints:

  • How many memory slots your Mac has;
  • How much you’re willing to spend.

Except for the models that don’t let you upgrade memory, I think all Mac laptops have two memory slots. Many desktops have four slots. However many you have, you will usually want to spread memory across your slots (but not necessarily all of them), instead of putting it all in one slot. There are two big reasons:

  • You’ll spend less money,
  • Your Mac will be a little bit faster.

That’s a nice combination!

The speed is simply because your Mac will perform a little better with matched pairs of memory modules. You can install single modules or unmatched pairs (one 2 GB + one 4 GB) but matched pairs will give you the best performance. But, remember, that’s assuming the same total amount of memory. As I mentioned in the video, my MacBook Pro runs faster with 6 GB (one 2 GB + one 4 GB) than it did with two 2 GB modules. The additional memory more than makes up for any performance hit caused by having unmatched modules.

Let me explain the cost decision using memory prices I just found for a 2011 iMac (which has four memory slots). These prices will likely be obsolete in a few months (fortunately memory prices almost always go down) but the general pattern will usually hold. Let’s say I want to put 8 GB of memory into this iMac. I have three options:

  1. One 8 GB module ($387.99)
  2. Two 4 GB modules ($63.99)
  3. Four 2 GB modules ($69.58)

As you can see 8 GB modules currently cost much more than 4 GB modules. Most importantly, they cost much more than TWO 4 GB modules. This is simply because making 8 GBs of memory fit into that small module is an expensive process. But, since they’ve been around awhile, 4 GB modules don’t have the same price premium compared to 2 GB modules. A 4 GB module actually costs less than two 2 GB modules, so buying four 2 GB modules makes no sense, especially since it would fill all your slots, leaving no room for more memory in the future.

Unless money is no object, we can see the size/price sweet spot in this case is to get our 8 GBs as two 4 GB modules. Heck, since this iMac has four slots, we could even get 16 GB (as four 4 GB modules) for still much less then one 8 GB module.

So why did I tell Dean that he needed to first check what memory modules he currently had? Well, he wanted a total of 8 GB, so if he already had one 4 GB module, he would have needed only one more. Unfortunately he had two 2 GB modules, which he had to retire since his MacBook Pro only has two slots.

Memory type and speed

Finally, when buying new memory for your Mac, make sure that you buy the same type (e.g., DDR2, DDR3) and speed (e.g., 667 MHz, 1066 MHz, 1333MHz) as your Mac’s original memory.

{ 1 comment… add one }
  • JOE HAGEDORN October 15, 2011, 6:20 am


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