PC Hardware

Universal Serial Bus (USB)

The newest addition to the PC bus collection, the universal serial bus (USB) connects external peripherals such as mouse devices, keyboards, joysticks, scanners, and digital cameras to the computer. The USB port is a thin slot; most new motherboards offer two, located near the keyboard. They can also be provided through an expansion card.

USB supports isochronous (time-dependent) and asynchronous (intermittent) data transfers. Isochronous connections transfer data at a guaranteed fixed rate of delivery. This is required for more demanding multimedia applications and devices. Asynchronous data can be transferred whenever there is no isochronous traffic on the bus. USB supports the following data transfer rates, depending on the amount of bus bandwidth a peripheral device requires:

  • 1.5 megabits per second (Mbps) for devices, such as a mouse or keyboard, that do not require a large amount of bandwidth.

  • 12 Mbps isochronous transfer rate for high-bandwidth devices such as modems, speakers, scanners, and monitors. The guaranteed data-delivery rate provided by isochronous data transfer is required to support the demand of multimedia applications and devices.

USB devices can be attached with the computer running. A new device will usually be recognized by the operating system, and the user will be prompted for drivers, if drivers are required. Bear in mind that USB is a new standard, and some early USB ports and chip sets do not properly support some newer devices. Problems with embedded USB ports are not generally worth repairing. It is usually better to install a new USB interface card.

USB 1.0

  1. Data rate 1.5 Mbits per second (Mbps)

USB 2.0

  1. High Speed

  2. Throughput up to 35 MB per second (280 Mbit per second)

  3. Support battery charging

USB 3.0

  1. Very High Speed

  2. 10 times faster than USB 2.0

  3. Supports data rate upto 512 MB per second (4 Gbit per second)

  4. Uses two unidirectional data paths one to receive and the other to transmit data