Product Specs: Technology: DDR3 SO-DIMM Density: 4GB (4096MB) RoHS: Yes Comp Count: 16 Depth: 256Mb Width: x64 Pin Count: 204-pin Op. Temp.: 0C to +85C Data Rate: DDR3-1333 Speed: PC3-10600 CL: CAS 9-9-9-24 Cycle Time: 1.875ns Voltage: 1.5V Comp Config: 128Meg x 8 ECC: Non ECC Module Ranks: Dual Rank Register: Non Parity. Low Noise 8-Layer PCB Meets and/or Exceeds Specifications. Fully Compliant with JEDEC specification. RoHS Certified Warranty Safe Upgrade. OWC Memory Lifetime Limited Warranty including the OWC Lifetime Advanced Replacement Program. Compatible with 27-inch iMac Models: Mid 2011 27 inch iMac Model ID: iMac12,2 (2.7GHz i5, 3.1GHz i5, 3.4GHz i7) and Mid 2010 27-inch iMac Model ID: iMac11,3 (2.8GHz, 2.93GHz, 3.2GHz, 3.6GHz); Compatible with 21.5 inch iMac: Late 2011 21.5-inch iMac Model ID: iMac12,1 (3.1GHz i3); and Mid 2011 21.5-inch iMac Model ID: iMac12,1 (2.5GHz i5, 2.7GHz i5, 2.8GHz i7); and Mid 2010 21.5-inch iMac Model ID: iMac11,2 (3.06GHz, 3.2GHz, 3.6GHz)