2500W AC Power Supply (WS-C6509-1300AC/2500AC) have nine slots each. Slot1 on the Cisco WS-C6509-1300AC/2500AC is reserved for the supervisor engine, which provides switching, local and remote management, and multiple gigabit uplink interfaces. Slot 2 on the Cisco WS-C6509-1300AC/2500AC can contain an additional redundant supervisor engine, which can act as a backup if the first module fails. If a redundant supervisor engine is not required, slot 2 is available for a switching module.