MacBook Pro with Retina Display review (mid-2012) - SlashGear
MacBook Pro: How to remove or install memory – Apple Support (UK)
MacBook Pro 15" Retina Display Mid 2012 Teardown - iFixit
Replace your 2009-2012 MacBook Pro HD with an SSD
16GB (2 x 8GB) DDR3 1600MHz PC3-12800 204-PIN SODIMM MEMORY RAM KIT FOR MACBOOK PRO (MID 2012) : Amazon.co.uk: Computers & Accessories
4GB Ram Memory (PC3L-12800, DDR3 1600MHz) for Apple MacBook Pro 15 inch A1286, 13 inch A1278 . iMac 21.5 inch A1418 , 27 inch A1419 , Mac Mini A1347 ( Mid 2012 - Mid 2015) - MacWave