Capacity: 4GB --- Technology: DDR3 --- Speed: PC3-10600 1333MHz CL9 --- ECC Type: Non-ECC Unbuffered --- Form Factor: 204-Pin Non-ECC SODIMM --- Voltage: 1.5V --- Backward Compatibility: Also compatible with 1066MHz --- System Compatibility: Lenovo ThinkPad W520 --- Replacement For: Lenovo 0A33299, 41R0642, 55Y3711, 55Y3717, 57Y3711, 78Y7385, 89Y9225 --- OWC DDR3 memory is Fully compliant with JEDEC specifications, ROHS compliant, providing a warranty safe upgrade. OWC Memory is the most cost effective and simple DIY upgrade you can install to unleash your Mac or PC's full potential and speed up overall responsiveness. Become a multitasking maven when you upgrade your Mac or PC with OWC Memory. Open more apps. Open larger files. Plus, work with multiple files all at the same time. We test every OWC memory module at our in house lab so you can upgrade with the confidence that your memory is built to last. We built your OWC Memory upgrade to meet or exceed the toughest industry specs to provide years of worry-free service. OWC recommends that all DIMMs be the same capacity, speed, and manufacturer to ensure optimal memory performance.