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How to buy ram for your imac
Buy no more than 16 gb of extra ram.
Imacs from 2011 , 2010, and late 2009 support a total of 16 gb of memory.
You can buy up to 4 different rams, or memory modules, for these imac models; however, they must not exceed a total of 16 gb in memory.
Buy ram with features that are compatible with your imac model. Imac models from 2011 and 2010 use the same type of ram; whereas the late 2009 models use ram with slightly different features.