Welcome to the Community.
These are the specifications for the WD Green (WD30EZRX) hard drive family:
http://www.wdc.com/global/products/specs/?driveID=927&language=1
As you may notice the rotational speed is not listed as 7200RPM, but rather as IntelliPower. This means the hard drive will only spin under 7200RPM when the device is under heavy load while decreasing its rotational speed in non-demanding circumstances down to 5400RPM. This is because the WD Green family of hard drives was designed for power-saving and low-noise above all else. If you would like a WD hard drive with a constant 7200RPM ratio, then I’d recommend the WD Blue and/or WD Black hard drive families.
