The Universal Serial Bus(USB) is a low cost, medium performance bus system allowing up to 127 devices to be attached to each USB host controller. USB is Operating System and computer hardware independent and was developed jointly by Compaq, Intel, Microsoft and NEC. Since it's introduction, it has been adopted by many computer and electronic companies worldwide as the base-standard for attaching and driving low speed external peripherals. Many of them are members of the USB implementers forum which is responsible for continuing development of the USB specifications.

The Simtec USB stack provides a standard way for applications and drivers under RISC OS to access devices attached to a USB bus.