What Is a USB Hub?

LaCie Data Bank Hi-Speed USB 2.0	6. USB Questions & Answers
User’s Manual	page 25

Technically, you can connect up to 127 devices to a single USB bus. For more than two devices, though, you must make new connections using a peripheral called a "hub.” A hub, which you hook up directly to a USB connector on your computer, usually has 4 or 7 output connections enabling you to connect the same number of peripherals. One of the hub's main functions is to regenerate signals that lose part of their strength as they are transmitted via the USB cable. By connecting yet another hub to a connector on the existing hub, you can then plug in a new set of peripherals and so on, up to a maximum of 127.

Some hubs have no power supply and others are self-powered. When you choose a hub, opt for the self-powered variety, as they have their own AC adapter. The most powerful hubs provide 0.5A of power to each port.

If you buy a hub, make sure that it supports per-port switching. This function prevents the entire chain of peripherals from freezing up if one of them is not working properly or is down.

Will Hi-Speed USB 2.0 Devices Work On USB Hubs And Vice Versa?

You can use your Hi-Speed USB 2.0 devices with USB hubs, but the peripherals will be limited to USB performance levels. There are Hi-Speed USB 2.0 hubs that are able to communicate in three modes: high-speed (480Mb/s), full-speed (12Mb/s), and low-speed (1.5Mb/s). Hi-Speed USB 2.0 is backwards compatible, so you will be able to connect USB devices to Hi- Speed USB 2.0 hubs; however, the USB devices will still maintain their normal performance levels (i.e. 12 Mb/s).

In order to achieve the fast data transfer rates of Hi-Speed USB 2.0, you must connect your Hi-Speed USB 2.0 device directly to a Hi-Speed USB 2.0 port on either a computer or hub.

Tech Note:

•Avoid using USB connectors found on certain peripherals such as keyboards. These are passive (or pass- through) connectors that lead to power loss and unstable operation.

•Only use USB cables shorter than 5 meters (approximately 15 feet). Using longer cables may cause the peripherals to malfunction due to excessive reduction in electrical signal strength.

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