The Supervisor Engine III hardware enables all three 1.2-Gbps backplanes in the Catalyst 5500 series switches to operate independently, providing 3.6-Gbps throughput (when traffic does not have to cross the backplane bus segments).The Supervisor Engine III boots differently from the earlier supervisor engines. The Supervisor Engine III boot process uses two images: ROM monitor and Catalyst 5000 family supervisor engine software. The ROM monitor is the first software to run when the switch is powered up or reset. Based on how the ROM monitor has been configured, the switch either stays in ROM monitor mode or loads the supervisor engine software (refer to the Software Configuration Guide for your switch for detailed information about using ROM monitor mode). A configuration register allows you to configure the ROM monitor, and the BOOT environment variable allows you to specify the location and filename of images to boot.