|Types of USB hubs
A USB hub is a device that can have other USB devices plugged into it. You use a USB hub when you want to connect more devices to your computer simultaneously and when you want to increase the distance between the devices and the computer. You can extend the number of available USB ports by plugging hubs together to form a large hierarchy of USB devices. You can also use a USB hub to extend the distance of an attached device.
There are two types of USB hubs: self-powered and bus-powered.
This type of hub has an AC adapter that provides external power to the hub. Your computer is a self-powered hub. To use the hub, you need to plug the adapter cord into an electrical outlet or power strip. The hub supplies its own power, so you can connect most USB devices to it. Typical self-powered hubs have four or seven USB ports.
Note: Apple recommends that you use self-powered hubs instead of bus-powered hubs for best performance.
This type of hub receives power from the computer or another self-powered hub, so you don't need to plug it into an AC outlet. You can plug low-powered USB devices, such as a mouse or joystick, into a bus-powered hub. The Apple USB keyboard contains a bus-powered hub.
IMPORTANT: You cannot connect two bus-powered hubs together because there's not enough power for both hubs or devices attached to them. To connect two hubs together, at least one hub must be self-powered. For this reason, you cannot connect an Apple USB keyboard to the USB port on another Apple USB keyboard. If you want to use two bus-powered hubs with your computer, connect each to a USB port on the computer or to a self-powered hub. If you use three or more hubs connected to one another, set them up so the chain alternates between the two kinds.
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