Added a couple more cores and 12 more gigs of ram to my T520 : r/thinkpad
8GB Stick for IBM Lenovo ThinkPad T Series T420 T420i T420s T520 T520i. SO-DIMM DDR3 Non-ECC PC3-10600 1333MHz RAM Memory. Genuine A-Tech Brand. at Amazon.com
Arch Memory 4GB 204-Pin DDR3 1333 MHz So-dimm RAM for Lenovo ThinkPad T520 4240-4AU at Amazon.com
Lot of (3) Lenovo ThinkPad T520 RAM Memory Cover Door w/ Screws 60Y550