PC Hardware in a Nutshell, Second Edition

USB Host Controller Interfaces

The intent of USB was to provide a standardized Plug-N-Play interface that would permit USB-compliant devices from any manufacturer to coexist peacefully with those from any other maker. The ball got rolling in September 1995, when 25 major PC companies announced the formation of a consortium to develop a non-proprietary, open Host Controller Interface (HCI) standard. This was necessary because the HCI was not defined in the USB specification itself. Although it would have been possible for each motherboard or chipset manufacturer to develop a proprietary USB HCI, that would have introduced serious compatibility issues between the multiple HCIs and USB peripherals. So, for the good of the industry and in the interests of interoperability, nearly all of the major players in the PC industry signed on to this initiative.

The HCI is the heart of USB, just as the chipset is the heart of a motherboard. In fact, the USB HCI is often referred to as the USB chipset. Just as the system chipset defines the functionality and capabilities of the motherboard, coordinates the working of other motherboard components, and arbitrates conflicting demands, a USB HCI chipset defines the USB and performs analogous services for connected USB peripherals.

The HCI may reside in any or all of three places:

Embedded in the motherboard chipset

All modern chipsets contain a USB 1.1 HCI embedded in the Southbridge. The quality and compatibility of the embedded HCI depends on the ...