Since the introduction of the first universal serial bus version in 1996, the USB interface has become the standard method for connecting input and output devices to PCs. Offering fast data transfers and the ability to provide power to devices, USB provides a big improvement over previous types of interface such as the serial or parallel ports.



  • The Universal Serial Bus
    • Universal serial bus refers to the way data is transmitted serially over two wires, using the voltage differential between the wires to transmit a zero or one. Using two wires helps to remove noise and interference in the cable, allowing data to be transmitted at faster rates. As most computers only have between two and eight USB ports, USB hubs are used to provide extra ports. A hub plugs into an existing port, and provides a number of extra sockets. Up to four external USB hubs can be daisy chained together, to connect up to a maximum of 127 devices to a single host controller.

    Plug and Play


    • USB was designed to make the process of connecting peripherals as user friendly as possible. By providing a standard interface, users do not need to worry about whether they have the relevant socket to connect a certain peripheral, and can purchase hardware knowing it will work on their computer. When a USB peripheral is plugged into a USB port, it can tell the computer exactly what it is and the driver it requires, allowing the computer to install the driver automatically for certain types of devices such as mice, keyboards or flash drives. USB devices are also hot swappable, allowing users to plug in or unplug devices while the computer is running, unlike previous types of port.

    USB Specifications




    • Over time, the USB specification has been steadily improved to allow for faster data transfers. The first version of the specification that was widely adopted, USB v1.1, had a maximum data rate of 12Mbits/s. Version 2.0, released in 2000, improved on this by a factor of 40, with a maximum data rate of 480Mbit/s allowing high-speed devices to function. The USB v3.0 specification introduces further improvements with a maximum data transmission rate of 5Gb/s, which is achieved by adding four extra wires named the "SuperSpeed" bus. More power is available to devices, with a new maximum of 900mA available. New power management features are available, including support of sleep and suspend modes for USB devices.

    USB Compatibility


    • One of the main features that has ensured the success of the USB specification is backwards compatibility. Older USB v1.1 devices function correctly with USB v2.0 controllers, ensuring that old hardware can be used until the end of its natural lifespan. Even the new USB v3.0 standard is backwards compatible, despite the extra wires and a redesigned plug, which means that USB v2.0 devices can still be used with a v3.0 controller and vice-versa.






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