Professional 4 Channel DVR with 1T HDD. iPhone Viewing, Real Time Recording, Motion Detection Recording Function with Sensitivity Adjustment, USB Backup, PTZ Control.When a program is being recorded, the 4 Channel DVR compresses and saves the streaming video into a digital movie format. This provides a buffer when pausing, rewinding and putting a program into slow motion. It also maximizes the space available on the hard drive. The basic features of a 4 Channel DVR Recorder are the same from platform to platform. Each allow you to record programs for playback, pause live television and rewind to a specific segment of the broadcast. The majority of recorders permit advance scheduling from 1 to 2 weeks and have the option to record an entire season of a particular show. DVRs function very much like a HDD DVR, but with a hard drive taking the place of a tape. A video signal is carried by a pair of cables which run from the wall to the converter box. The lines each carry a unique video signal, which is what allows a viewer to watch one program while recording another. One cable will leave the back of the DVR and run to the television, providing the audio and video of the broadcast.Don't hesitate to buy it, it will take you into an elegant world.