MacBook Pro 13" Unibody Early 2011 RAM Replacement - iFixit Repair Guide
8GB RAM Upgrade for 2011 MacBook Pro & Mac Mini Core i5 & i7 – $34 | OSXDaily
Samsung ram Memory 8GB kit (2 x 4GB) DDR3 PC3-12800,1600MHz for 2012 Apple MacBook
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
MacBook Pro: How to remove or install memory - Apple Support