HP ProBook 4540s C6Z37UT Notebook PC - 3rd generation Intel Core i5-3210M 2.5GHz, 4GB DDR3, 500GB HDD, DVDRW, 15.6 Display, Windows 7 Pro 64-bit / Windows 8 Pro 64-bit at TigerDirect.com
parts-quick 8GB DDR3 Memory for HP Compaq ProBook 4540s PC3-12800S 204 pin 1600MHz SODIMM Laptop Compatible RAM at Amazon.com