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Extensible Host Controller Interface
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<p>The eXtensible Host Controller Interface (xHCI) is a technical specification that provides a detailed framework for the functioning of a computer's <a href="/facts/Host_controller/nQbbDHF2">host controller</a> for <a href="/facts/Universal_Serial_Bus/XcIKWLyg">Universal Serial Bus</a> (USB). Known alternately as the <a href="/facts/USB_3.0/WTnYm1IS">USB 3.0</a> host controller specification, xHCI is designed to be backward compatible, supporting a wide range of USB devices from older USB 1.x to the more recent USB 3.x versions. </p><p>Distinct from its predecessors, the <a href="/facts/Open_Host_Controller_Interface/NKuGNs02">Open Host Controller Interface</a> (OHCI) and the <a href="/facts/Universal_Host_Controller_Interface/NKuGNs02">Universal Host Controller Interface</a> (UHCI), xHCI offers several technological improvements. Specifically, it is designed to handle multiple data transfer speeds (low, full, high, and SuperSpeed) within a single unified standard. This makes it more efficient in managing computational and power resources, a feature particularly beneficial for mobile devices with limited power capabilities like tablets and smartphones. Additionally, xHCI simplifies the architecture needed to support a mixture of low-speed and high-speed devices, which streamlines the development of drivers and system software. </p><p>xHCI marks a significant improvement over its predecessors, the Open Host Controller Interface (OHCI), the Universal Host Controller Interface (UHCI) and the Enhanced Host Controller Interface (EHCI), in several key ways: </p> <ol><li>Multi-Speed Support: Unlike OHCI, UHCI and EHCI, which were limited to specific USB speeds, xHCI is capable of managing multiple data transfer speeds—low, full, high, and SuperSpeed—under a single standard. This eliminates the need for multiple host controllers or complex switching mechanisms when dealing with various types of USB devices, thereby improving efficiency.</li> <li>Power Management: xHCI includes advanced power management features that allow for selective suspension of USB devices and more granular power distribution. This is especially beneficial for mobile devices with limited battery life, such as tablets and laptops, as it helps to maximize power utilization and extend battery life.</li> <li>Streamlined Architecture: xHCI's architecture is designed to be simpler and more straightforward, reducing the complexity of driver development. In older architectures like OHCI, UHCI and EHCI, supporting a mix of low-speed and high-speed devices required complicated algorithms and multiple transaction translators. xHCI simplifies this by integrating these functions into the host controller itself, thus easing the burden on system software and driver developers.</li></ol> <p>By enhancing support for multiple speeds, optimizing power management, and simplifying the underlying architecture, xHCI serves as a more efficient and unified standard for USB host controllers. </p>