A simplex machine is best for applications where simply recording is important. While in record mode, simplex machines are unable to display multi-screen images (i.e. quad, 9 way, and 16 way split).

A duplex machine is preferable if an operator is watching the system (for example, a security guard). Screen splits and user selected images can be provided by a duplex machine without impacting what is recorded on the recorder. It is possible to record and replay simultaneously if you use two recorders.