- Revision 1.0 released on January 15, 1996, introduced a
low-speed transfer rate of 1.5 Mbit/s and a full-speed transfer rate of 12
- Revision 1.1 released on September 23, 1998, introduced
the improved specification and was the first widely used version of USB.
- Revision 2.0 released on April 27, 2000. The major
feature of revision 2.0 was the addition of a high-speed transfer rate of
- Revision 3.0 released on November 17, 2008, brings significant performance enhancements to the USB standard while offering backward compatibility with the peripheral devices currently in use. Legacy USB 1.1/2.0 devices continue to work while plugged into new USB 3.0 host and new USB 3.0 devices work at USB 2.0 speed while plugged into USB 2.0 host. Delivering data transfer rates up to ten times faster (the raw throughput is up to 5.0 Gbit/s) than Hi-Speed USB (USB 2.0), SuperSpeed USB is the next step in the continued evolution of USB technology.
- Single connector type: USB replaces all the different legacy connectors with
one well-defined, standardized USB connector for all USB peripheral
devices, eliminating the need for different cables and connectors and thus
simplifying the design of the USB devices. So all USB devices can be
connected directly to a standard USB port on a computer.
- Hot-swappable: USB devices can be safely plugged and unplugged as
needed while the computer is running. So there is no need to reboot.
- Plug and Play: Operating system software automatically identifies,
configures, and loads the appropriate device driver when a user connects a
- High performance: USB offers low speed (1.5 Mbit/s), full speed (12
Mbit/s) and high speed (up to 480 Mbit/s) transfer rates that can support
a variety of USB peripherals. USB 3.0 (SuperSpeed USB) achieves the
throughput up to 5.0 Gbit/s.
- Expandability: Up to 127 different peripheral devices may
theoretically be connected to a single bus at one time. (And computers can
have more than one bus.)
- Power supplied from the bus: USB distributes the power
to all connected devices eliminating the need for external power source
for low-power devices. High-power devices can still require their own
local power supply. USB also supports power saving suspend/resume modes.
- Easy to use for end user: A single standard
connector type for all USB devices simplifies the end user's task at
figuring out which plugs go into which sockets. The operating system
automatically recognizes the USB device attachment and loads appropriate
- Low-cost implementation: Most of the complexity of the USB protocol is handled by the host, which along with low-cost connection for peripherals makes the design simple and low cost.