Apple recommends installing pairs of memory sticks with matched sizes to allow for dual-channel memory interface.
However, some people believe that it's also important not only to match the sizes of the two RAM sticks, but to install what manufacturers sell as "matched pair kits". Others disagree.
http://forums.macrumors.com/showthread.php?t=392843:
The tolerances of two single memory modules can be different. With a matched pair the tolerances are supposed to be close to the same if not the same.
I don't think their is a difference, at least in the real world. Two modules of the same part number should work just fine. Matched pairs seems to be little more than marketing and paying a 'tax' for intangible 'peace of mind'
You can get a matched pair by buying 2 singles of the same ram too..
http://www.dslreports.com/faq/9231:
Two modules of the same model/brand purchased from the same vendor at the same time is essentially as likely to work properly in a dual channel configuration as is a dual channel kit.
http://wiki.answers.com/Q/What_are_the_advantages_to_buying_DDR_RAM_in_packaged_pairs?classic=true:
Typically the chips are the same production batch and that increases the likelihood that the paired modules will work approximately at the same speed, therefore being detected (and usable) as dual-channel.
To summarize:
- Some people believe that buying two individual sticks of RAM from the same manufacturer with the same specifications is no different than buying a paired kit.
- Some people believe that buying a paired/matched kit provides some performance or reliability benefit as compared to buying two individual sticks of RAM from the same manufacturer with the same specifications.
Which is true?