4GB Memory Upgrade for Dell Inspiron 15 (3521) DDR3L 1600MHz PC3L-12800 SODIMM RAM (PARTS-QUICK BRAND) Capacity: 4GB Form Factor: 204 pin SODIMM Speed: PC3L-12800 1600MHz 1.35v Low Voltage Low Power Halogen Free; ROHS; Warranty: Lifetime