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A USB system is composed of three areas:
- USB interconnect (cables, ports)
- USB devices (keyboard, storage, controller)
- USB host (Laptop, computer)
# Hosts
There is only one host in any USB system. The USB interface to the host computer is referred to as the Host Controller. The Host Controller may be implemented in a combination of hardware, firmware, or software. A root hub is integrated within the host system to provide one or more attachment points.
# Devices
USB devices are one of the following:
- A hub, providing additional attachment points to the bus
- Functions that provide capabilities to the system (speakers, keyboard)
# Interconnects
# Protocol
A Universal Serial bus is strictly a *polled* bus, meaning the