According to OWC, Apple has changed how the main hard drive SATA power connector, and the firmware on the hard drive. The SATA power connector has switched from a normal 4-pin power to 7-pin power that combines temperature monitoring and some other kind of connectivity between the main board and the drive. Because of this you will not be able to upgrade the HDD yourself and half to go with Apple. If you try to replace with a 4-pin HDD it will cause AHT (Apple Hardware Test) to fail and not essentially boot, and cause the HDD fan's to spin at 100% speed. Let's hope this is something that they are testing and not moving to other lines of mac's.