what is the maximum number of usb devices that can be attached to a single usb controller
USB hub Most USB hubs use one or more integrated controllers (ICs), of which several designs are available from various manufacturers. Most support a four-port hub system, but hubs using 16-port hub controllers are also available in the industry.[citation needed] The USB bus allows seven cascading tiers of ports. The root hub is the first tier, and the last devices are on the seventh tier, which allows 5 tiers worth of hubs between them. The maximum number of user devices is reduced by the number of hubs. With 50 hubs attached, the maximum number is 127 âˆ’ 50 = 77.[6]