8GB (4GBx2) Team High Performance Memory RAM Upgrade For HP - Compaq ProBook 6455b 6540b Laptop. The Memory Kit comes with Life Time Warranty. at Amazon.com
HP ProBook 6540b Notebook PC | HP® Customer Support
Arch Memory 4GB 204-Pin DDR3 1333 MHz So-dimm RAM for HP ProBook 6540b at Amazon.com
Arch Memory 4GB 204-Pin DDR3 1333 MHz So-dimm RAM for HP ProBook 6540b at Amazon.com