A simplex multiplexer works the same way a quad processor works. It will display all of your cameras on one screen, but will not record all cameras when viewing in full screen mode. A duplex multiplexer will record all cameras continuously whether in full screen or multi camera modes. A triplex multiplexer will record all cameras continuously whether in full screen, multi camera or play back modes. Furthermore, after recording, any camera can be viewed at full screen regardless of what mode it was recorded in.