Tutorial: How to Upgrade T410/T420/400 Thinkpad Laptop to 8GB - YouTube
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
OFFTEK 4GB Replacement Memory RAM Upgrade for IBM-Lenovo ThinkPad T420 (DDR3-12800) Laptop Memory at Amazon.com