I’ve heard a lot of questions about whether or not RAM in the Intel-based Macs needs to be installed in matching pairs. Here’s the real answer: Your mileage may vary.

It depends on what you do and it also depends on which Mac you have. If you have a Mac Pro, you have to install perfectly matched pairs. 2 identical DIMMs from the same vendor. If you have an iMac or a MacBook Pro, which have separate video RAM for the graphics processors, and you are not running applications which would significantly benefit from the increased memory bandwidth of the dual-channel memory architecture (most of us aren’t) then you don’t need matching pairs. If you have a MacBook, Mac mini, or low end iMac with the Intel graphics processor that uses a portion of the main memory, having matching pairs is a good idea. Non-matching pairs in these machines can impact video performance due to the decreased RAM performance.

The basic idea of dual-channel memory is this: Matching pairs creates a wider pipe for your data to use. Unmatched RAM uses a single memory channel, kind of like an inch wide pipe. Matching the RAM in a pair doubles the bandwidth, creating a hypothetical 2 inch wide pipe, which more than doubles the capacity. If you are using software like Final Cut Pro, Aperture, or Photoshop, you should see a difference.

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