It is a 4CH DVR CCTV Security System 3G Mobile 420TVL Sony COMS Camera SATA2.0 500GB HDD. I tried to format the hard drive but get the message it is not detected. I don't have a computer to try the hard drive in but it does try to run when the system is first turned on, I had the cover off and heard it whirl but then stops. Somebody suggested once that maybe the power supply is not strong enough to run the hard drive, I am using the power supply that came with the system, it is a 110-240 volt-50/60lhz DC 12v 2A power supply cord.