USB is an acronym that every person that uses computers and gadgets knows, even if they don't know what it stands for.  The Universal Serial Bus is a plug-and-play interface between a computer and many different devices, such as mobile phones, peripheral devices, printers, digital cameras, etc. It was developed at the end of the last century by Compaq, IBM, DEC, Intel, Microsoft, NEC and Northern Telecom and is a technology available without charge for all computer and device vendors.

USB is popular because of some very useful features:

• "Hot-swapping" allows the user to attach or remove a peripheral device without the need to shut down and restart the computer which automatically detects the peripheral and configures the necessary software
• USB also lets the user connect many peripherals at the same time. Multiple USB ports and USB hubs support the "daisy-chaining" of multiple peripheral devices together
•  USB can be used to distribute electrical power to many peripherals. The computer automatically senses the power that's required and delivers it to the device. This useful USB feature eliminates the need to carry around multiple power supply boxes for the different gadgets that we use
• USB connections allow data to flow both ways between the PC and peripheral

The increased number of different devices and requirements for fast transfer of data between them and a computer has been pushing the industry to develop faster USB interface specifications.

While USB 1.0 is defined by a low speed rate of 1.5 Mbit/s intended primarily to save cost in low-bandwidth human interface devices such as keyboards, mice, and joysticks, USB 1.1 supports a full speed rate of 12 Mbit/s.

USB 2.0 was introduced in 2001 and provided a significant improvement in the communication speed - a hi-speed rate of 480 Mbit/s. All USB 2.0 devices are backward compatible with USB 1.1 and the connectors used are identical. The communications are half-duplex, i.e. bi-directional, in one direction at a time over a twisted-pair cable.

The USB 3.0 Promoter Group announced on November 17, 2008 that version 3.0 of the specification had been completed and made available to the USB Implementers Forum (USB-IF), the managing body of USB specifications, allowing hardware developers to implement it in future products.

This is a SuperSpeed USB with a rate of 4.8 Gbit/s. Other than the significantly higher speed, USB 3.0 uses full duplex operation, i.e. simultaneous communication in both directions. This requires increase in the number of wires and new connectors that are generally backwards compatible, but include new wiring.