Page "USB hub" Paragraph 26

Most USB hubs use one or more integrated controller ICs, of which several designs are available from various manufacturers.

Most support a four-port hub system, but hubs using 16-port hub controllers are also available in the industry.

although some 16-port hub actually consist of four cascaded four-port controllers.

Additional features on some hub controllers include control of port LEDs ( sometimes automatic, sometimes under control of the host PC ) and PS / 2 to USB conversion for mice and keyboards.