There are only two USB ports on an iMac, yet the iMac can support up to 127 USB devices. The means to achieving this feat is the hub . A hub, like the one pictured in Figure 9-4, allows a number of USB devices to be plugged into it. The hub, in turn, is then plugged into one of the USB ports on the iMac. The hub shown in Figure 9-4 is a four port hub, so up to four peripherals could be plugged into it.
Hubs come with different numbers of ports, with four and seven ports being common.
Figure 9-5 provides a look at how a hub makes it possible to connect a few devices to an iMac using just one of the iMac's USB ports. Since a hub typically provides seven or fewer ports, you may be confused as to how a hub makes it possible to connect up to 127 devices to a single iMac. So another hub can be plugged into a port on an existing hub. Figure 9-5 Data flow between an iMac and several USB peripherals. A hub can be likened to the powerstrip that people plug computer equipment or stereo components into.