4GB Team High Performance Memory RAM Upgrade Single Stick For HP - Compaq ProBook 4411s 4415s 4416s 4510s (DDR2) Laptop. The Memory Kit comes with Life Time Warranty. at Amazon.com
KINGSTON Genuine Class Memory DDR2 4 GB (Dual Channel) PC (4GB 800MHz) - KINGSTON : Flipkart.com
Corsair SODIMM, 4GB, DDR3, 1600MHz, CL11, Single stick (CMSO4GX3M1A1600C11)
Why isn't there a single technology company that produces DDR2 4GB above? - Quora