Think of the Digital Video Recorder (DVR) as a VCR that can display live video footages from multiple camera sources simultaneously and record them on a hard disk. Unlike VCR, there are no cassettes or tapes to change. You can search & review any recorded surveillance video based on date, time, camera, events, etc. You can playback video from single or multiple cameras simultaneously. For higher end DVR, you can also playback the recording while the recording is still on-going.