Arch Memory 2 GB (1 x 2 GB) 200-Pin DDR2 So-dimm for Lenovo ThinkPad R52 Pentium M/Celeron M 1850, 1858, 1859 Series RAM Arch Memory is a Registered Trademark of Arch Computer, LLC Pins: 200 Pin Data Transfer Rate: 533Mhz System Type: Laptops Bus Type: PC-4200