The bus breaks out into a star from each hub. Hubs Hubs serve as connection points for devices. Most free standing external hubs provide 4 or 7 ports. Devices Devices connect to hubs and provide expanded functionality to the computer. Devices connect to the host and transfer data at either the 1.5 or the 12 Mbps connection speed.
Devices can only connect to hubs.
Devices cannot connect directly to devices, but looks can be deceiving, since some devices are combined with hubs in the same physical enclosure, in what is known as a compound device. A USB keyboard is a typical example when it has a Type A socket for connecting a mouse for instance. Most people shouldn't have a problem with this limit, although devices can add up faster than expected. For example, a keyboard with a built-in trackball counts as two devices. This can be tricky to debug sometimes, since hubs can be hidden in CPU cases, displays, keyboards, etc.