The Hard Drive Upgrade Kit with Digital Thermal Sensor Cable from OWC (Other World Computing) is designed for all 21.5" and 27" Apple iMac 2011 models. You can replace the original hard drive with a new one having a capacity up to 4.0TB, for up to eight times more storage capacity. This plug and play solution allows the use of any 3.5" serial ATA hard drive in your iMac. Further, this maintains proper system fan speed control via the Apples built in SMC, with no software hacks. It is fully compatible with Apple diagnostic testing.