CCTV hardware is what enables a surveillance system to function as a whole. CCTV equipment such as switchers, quad compressors, multiplexers, and duplex multiplexers are what enable multiple cameras to be recorded onto one VCR tape and or viewed on multiple monitors. A switcher enables multiple cameras to sequence from one camera to the next and once finished cycling starts at camera one again.
Switchers simply alternate through attached cameras.
Quad units allow you to monitor and record up to 4 cameras at once. Multiplexers allow you to record and view multiple cameras on one VCR tape.