This is a Apple branded 25GB 3.5" 7,200rpm SATA hard drive which is compatible with all iMac ranges from the late 2009 model up to the Retina 5K late 2015 model. Apple use multiple manufactures for their hard drives, this listing is for a Western Digital.

Because of the need for the internal firmware to match between the logic board and the hard drive on these ranges of iMac, standard drives cannot be fitted without altering the fan speed. (This can be resolved with an app such as Macs Fan Control, or by fitting an external sensor inside the machine.) Only Apple original drives are compatible as they are.

Hard Drive EEE Codes:

DJJD