Universal Serial Bus – has been evolving. It is common to have four or six USB connectors on a PC or laptop computer. These are usually USB 2.0 (introduced in 2000), identifiable by the ports which are generally black. The maximum transfer rate is 480 Mb/s which offers potentially useful connectivity for media applications on PCs and Macs. It is very cheap and widely used for connecting PC peripherals. It is a PAN, and so the service provided to any one device depends on their specification and what other connected devices are doing. Actual speeds achieved for bulk data transfers are about 300 Mb/s – but this is likely to rise.

The newer (2008) USB 3 ports are generally blue. They add a new transfer mode called SuperSpeed working at up to 5 Gb/s, more than ten times faster than USB 2. It is also full duplex (USB 2 is half duplex) meaning it can both simultaneously transmit and receive at full speed – making a total of 10 Gb/s I/O. USB 3.1 was released in 2013 which doubled the top speed to 10 Gb/s, with full duplex.

See also: IEEE 1394