PCIUSB

PCIUSB is a term used to describe USB host controller hardware that resides on a PCI bus within a computer system. In this usage, a PCIUSB device provides the USB host interface to the rest of the system, allowing the CPU to manage USB ports and connected devices through the PCI infrastructure.

A PCIUSB controller exposes its configuration through the PCI configuration space and uses PCI memory-mapped I/O regions and interrupts to communicate with the host processor and the operating system's USB stack. It is responsible for device enumeration, power management, and data transfer scheduling between USB peripherals and the host.

Historically, PCI-based USB controllers implemented the USB 1.1 UHCI and OHCI standards, later adopting USB 2.0's EHCI interface. With the rise of USB 3.0 and beyond, the industry increasingly moved to controllers based on PCI Express with xHCI, reducing the prominence of traditional PCI-bound PCIUSB devices in new designs.

Operating systems include drivers for standard USB host controllers that recognize these devices, enabling automatic device enumeration, driver binding, and seamless use of USB peripherals. Basic firmware or BIOS/UEFI initialization may also provide early USB support on systems with PCI USB hardware.

Today, PCIUSB is largely a historical or legacy term, with modern USB host controllers typically implemented on PCI Express. Nonetheless, PCI-based USB controllers persist in older machines and some embedded contexts where PCI remains in use.