The ports on the PC are known as “root ports,” and the root ports are designated as “tier 1.” Tiers 2 through 6 represent additional levels made possible by hubs, and tier 7 is the final level of devices supported by a hub at Tier 6.įigure 1. The total bandwidth of the downstream ports together can’t be greater than the bandwidth available on the upstream port. There are typically four downstream ports on each hub, but other numbers of ports on a hub are possible as well. With the second hub connected to the first, USB 2.0 and USB 3.0 allow up to five levels of hubs to be cascaded together (Fig. To obtain the speed and power benefits of USB 3.0, the hubs and interconnecting cables will all also need to be USB 3.0 compliant, including USB 2.0 support for USB 2.0 devices. Connecting two hubs into the topology enables support for all of the additional USB devices, and there may even be some USB ports still available for more devices.

The USB 2.0 ports might be used for a USB keyboard and USB mouse, but the user may have far more than two additional USB devices to connect to the PC at the same time, and many of those might be capable of USB 3.0 operation. But what can USB 3.0 users do when they need more USB 3.0 ports than their PC or docking station provides? External USB 3.0 hubs are the answer.ĭownload a special PDF version of this article, which is exclusive only to Electronic Design community members.Ī typical host PC might have two USB 2.0 ports and two USB 3.0 ports. These benefits are achieved while maintaining functional and mechanical compatibility with USB 2.0 devices, hubs, and host ports. Market acceptance of USB 3.0 has been increasing steadily because of its many advantages over USB 2.0, including far higher speed (up to 5-Gbit/s raw bandwidth), higher power availability (up to 900 mA per port), and better power management through more levels of power reduction when maximum power isn’t needed.

Usb 2 vs usb 3 plug