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MacBook Pro: How to remove or install memory - Apple Support
parts-quick 8GB Memory for Apple MacBook Pro 13 inch (Mid 2012) PC3-12800S 1600MHz DDR3 SODIMM Compatible RAM Brand
MacBook Pro review (13-inch, mid-2012) | Engadget
OWC 16GB (2x8GB) ram Upgrade PC3-12800 DDR3L 1600MHz sodimm 204 Pin CL11 Memory Upgrade Kit Compatible with Late iMac, Mac Mini, and MacBook Pro Computer at Amazon.com
OFFTEK 4GB Replacement Memory RAM Upgrade for Apple MacBook Pro 2.5GHz Intel Core i5 - (13-inch) (DDR3) (Mid-2012) (DDR3-12800) Laptop Memory
How to upgrade the RAM on your 13-inch MacBook Pro