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Unless you get the 27" iMac, you won't be upgrading anything. Memory on the 21.5" is soldered in, assuring you have to pay Apple extortionist pricing for a memory upgrade.
 
I used Crucial for my current iMac and I have never had a problem with it.

Good prices and good RAM from my experience.

Like the other poster pointed out, you will need to go for a 27" model if you want to upgrade the RAM yourself ...
 
Unless you get the 27" iMac, you won't be upgrading anything. Memory on the 21.5" is soldered in, assuring you have to pay Apple extortionist pricing for a memory upgrade.

I guess I should have been more specific lol but yes I'm planning on getting the 27 inch iMac :)
 
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