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== History ==
The Open Host Controller Interface (OHCI) specification was defined by a consortium of companies (Compaq, Microsoft, and National Semiconductor) as open specification to support USB 1.0 devices. The Universal Host Controller Interface (UHCI) refers to a specification that [[Intel]] originally defined as a proprietary interface to support USB 1.0 devices. The UHCI specification was eventually made public, but only after the rest of industry had adopted the OHCI specification.
The EHCI specification was defined by Intel to support USB 2.0 devices. The EHCI architecture was modeled after the UHCI and OHCI controllers, which required software to build the USB transaction schedules in memory, and to manage bandwidth and address allocation. To eliminate a redundant industry effort of defining an open version of a USB 2.0 host controller interface, Intel made the EHCI specification available to the industry with no licensing fees. This licensing model was continued for Intel's xHCI specification, however with a greatly expanded industry contribution. Over 100 companies have contributed to the xHCI specification. The [[USB Implementers Forum]] (USB-IF) has also funded a set of xHCI Compliance Tests to maximize the compatibility of the various xHCI implementations.
=== Version history ===
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