A quad is an accessory to your surveillance system that splits a video monitor into 4 screens. Without a quad you would only be able view one camera at a time on a single screen (or you could have a different screen for each camera, but this gets expensive and bulky). A quad is only needed when you are using more than one camera and using a VCR or VISEC to record, or when you are only monitoring and not recording at all.
These are high-resolution, real-time quads that support up to 4 cameras. You also have the ability to playback and zoom in on recorded video. There are other products out there that can split a screen more than four ways. However, video quality worsens the more ways you split a screen. A quad is not needed when using a DVR (Digital Video Recorder, at the bottom of this page) to record because DVRs have a built-in quad.
Features: Full duplex allows transfer of recording and playback video at the same time. 2x2 zoom, 60 frames per second, Real time clock, Title generator, On-screen display, No boarder for full quad display, 2H adaptive comb filters for Y/C separation.