Because so many peripheral devices use the USB interface, you will probably run out of available USB ports before you run out of devices you want to attach to your Mac. That's where a USB hub comes in.
To learn more about the USB interface, see "USB," p. 630.
A USB hub expands the number of USB ports that are available on your Mac; USB hubs are one of the simpler devices you will use. USB ports offer the following features:
Number of ports The number of ports a USB hub offers determines the number of devices you can attach to it. Typical USB hubs offer four ports, but some offer more than that (such as seven ports).
Sometimes the number of ports offered by a hub can be a bit deceiving. Remember that you have to use one port to connect the hub to your Mac or to another USB hub. Some hubs count this "upstream" port, but others do not. For example, some four-port hubs allow you to connect only three USB devices because one port is required to connect the hub to your Mac or to another hub. Other four-port hubs provide an additional port for the upstream connection so that you can actually connect four devices to them.
Self-powered or bus-powered Some hubs get the power they need from an external power supply (they provide this power to the devices that are attached to them if needed). Others take power for the hub and the USB devices from the USB bus itself.
Although most Macs include two or more USB ports, you can often find additional ports in the other devices attached to your Mac. For example, the Apple Pro keyboard has two USB ports built into it. Some of the Apple monitors, such as the 22-inch Apple Cinema Display, also include additional USB ports. Make sure that you account for these available ports before adding a dedicated USB hub to your system.
Choosing a USB hub is mostly a matter of deciding the number of USB devices you want to be able to connect to your Mac at the same time (see Figure 24.3).
Remember that USB is hot-swappable, meaning that you can connect and disconnect USB devices at any time. There are many devices you will need to connect only periodically, such as a digital camera. So you don't really need a USB port dedicated to every USB device you have?just those you want to always be available. Having one or more extra ports above that number enables you to add other devices as you need them.
Next, you should decide whether you want a self-powered or bus-powered hub. Because some devices take their power from the USB interface, you should get a USB hub that is capable of providing its own power (many hubs can operate either on their own power or on power from the USB bus). If you are going to use the hub primarily on the move, such as with your PowerBook, a bus-powered hub might be a better choice (it will be smaller than a powered hub).
Some hubs offer other features that aren't required, but that can be useful. For example, some hubs provide status lights for each port. These lights show you when a device is actively using the port; this can be helpful when you are troubleshooting problems with a specific peripheral device.
Installing a USB hub is quite simple. You just attach its uplink port to a USB hub on your Mac or on another USB hub. Then, attach each device to a port on the hub. If the hub is self-powered, attach its power source. That's it.
There isn't anything to using a USB hub, either. They just work.