Host Controllers

Today the USB host controller is integrated on most motherboard chipsets. Older boards which are not equipped with such a controller can be upgraded by PCI cards with such host controllers. All these controllers are compatible with either the Open Host Controller Interface (OHCI by Compaq, Microsoft and National Semiconductor) or the Universal Host Controller Interface (UHCI by Intel [7]) standard. Both types have the same capabilities and USB devices do not have to care about the host controller. Basically the hardware of UHCI is simpler and therefore it needs a more complex device driver, which could cause slightly more CPU load.