iMac RAM upgrade: Here's an affordable way to improve multitasking - CNET
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Apple MC309LL/A 21.5" iMac Computer Core i5 2.7 GHz 4GB RAM 1TB HD Mid-2011 | RecycledGoods.com
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Apple® iMac with Intel® Core i3 3.06GHz, 4GB RAM, 500GB HDD + Keyboard/Mouse - Pick Your Plum
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