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Pairing iMac RAM?

M

Mightee

macrumors member
Original poster
Feb 25, 2004
90
8
All right, this might be a silly question. I just bought myself a new i5 2.5" iMac, and I swapped out the two 2GB RAM modules for a pair of 4GB chips. The 2GB are currently sitting in my desk drawer.

But since the iMac has four slots, could I just pop those two in as well for a total of 12GB? I seem to remember pairing being a big issue once upon a time, but I'm not sure that's still the case. Are there issues with this? Should I just wait a little bit until I can buy two more 4GB DIMMs? Or can I just slide those two old ones into the bottom slots and call it a day?

Thanks folks.
 
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My Late 2009 iMac came with 2 x 2GB memory. I picked up a pair of 1GB sticks for $20 locally off craigslist and threw them in there with the stock to take it to 6GB. It works flawlessly and all 6 register just fine. Once Lion comes out I'll probably have to upgrade my MacBook from its original 2GB, so I'll probably buy 2 x 4GB, put that and the 2 x 1GB in the iMac, and move the 2 x 2GB into the MacBook. It works out great that they use the same type :D
 
Mightee said:
Thanks! So when did pairing become unimportant? There's no particular order in which I should arrange the DIMMs?
Click to expand...

I'm not an expert on this, but I believe if you go with the 12GB you will not be running Dual-Channel mode. That's probably not a big deal, from what I've read dual-channel memory boosts speeds by only 3%-6%. Usually the benefit of having more RAM trumps running in dual-channel mode. So go for the 12GB.

I've also read that you should install the larger DIMMs in the first slots because those slots are addressed first by the CPU.

slot 1: 4GB
slot 2: 4GB
slot 3: 2GB
slot 4: 2GB
 
I've been trying to figure this out for a couple days. It's confusing, and there's plenty of contradictory information out there. Here's something to contradict my post from ten minutes ago. The way I read it, it may be possible to achieve dual-channel with this configuration.

slot 1 (ch. A, DIMM 0): 4GB
slot 2 (ch. A, DIMM 1): 2GB
slot 3 (ch. B, DIMM 0): 4GB
slot 4 (ch. B, DIMM 1): 2GB

link: http://www.intel.com/support/motherboards/desktop/sb/cs-011965.htm#dual

Unfortunately, there does not seem to be any easy way to confirm if an iMac is running dual-channel mode. You can run Xbench tests with various RAM configurations and the results may lead you to the "best" configuration. Or you can install Windows, and using Bootcamp, run an application called Everest. That application will tell you if the computer is running dual-channel.
 
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