A CCTV system depends on a reliable recording device to store surveillance videos. A DVR (Digital Video Recorder) acts as the hard drive in a security camera system. The most important features of a DVR include the memory capacity, inputs, and outputs. The memory usually ranges between several hundred GBs to more than 1 TB. Users should estimate how many hours of video footage they need stored on a DVR. As with other recording media, the videos could be erased or overwritten with new footage. The latest DVRs should be compatible with common video sources such as HDMI, VGA, DVI, and A/V connections, which are used to connect to HDTVs and computers.