Specs Lenovo ThinkPad T420 DDR3-SDRAM Notebook 35.6 cm (14") 1366 x 768 pixels 2nd gen Intel® Core™ i5 4 GB 320 GB HDD Windows 7 Professional Black Notebooks (NW464UK)
Lenovo Thinkpad T420: Another excellent, inexpensive Linux laptop | Open-Source Routing and Network Simulation
HD] Installing RAM on a Lenovo Thinkpad T420 Guide T410 T400 - YouTube
RAM Upgrades Overview | Lenovo ThinkPad T420 T-Series - max up to 16GB