Basic : simply supply IT equipment with multiple AC outlets. It can be used in an A/B Circuit configuration but does not supply any extra features other than power distribution.
Metered : have a LED status display built into unit itself. This feature allows at-the-rack current monitoring for each unit as a whole. This feature becomes very valuable when one wants to make sure. They do not overload circuit or when load balancing an A/B feed installation.
Monitored : typically include the feature sets of the metered and switched products in a single unit. It also has the ability to remotely monitor the state of the distribution unit and in some models, the ability to see the current draw down to the outlet level and report history trends. Access to these models is typically accomplished through dedicated remote access software, direct web interface, SNMP or serial (RS 232) menu. This type of PDU becomes very valuable in situations where up to the minute monitoring of power draw with in a rack is required.
Switched : typically includes the features of the metered PDU as well as the ability to remotely control the on/off state and reboot capabilities of each outlet contained in the unit through a web interface or serial (RS 232) menu. Certain models of switched PDU allow the user to “lock off” any number of outlets to prevent unwanted connection of equipment that might overload the circuit.