This read-only INTEGER reports which system backplane bus speed the chassis is built with, either bus-800-mbit(1) or the faster bus-1p6-gbit(2). An administrator checks it to know whether the chassis has the throughput headroom needed for higher port-density or higher-speed modules before installing them. For example, before adding a new high-throughput IOM, the admin polls hwSysBus and confirms it reads bus-1p6-gbit(2) rather than the slower 800 Mbit variant.