USB Definition

USB (universal serial bus) is a widely used standard for high speed plug-and-play serial connections between computers and external peripheral devices (such as disk drives, memory sticks, keyboards, mice, digital cameras, scanners, network devices and printers) as well as among an increasingly great variety of other electronic products as well.

USB is universal in the sense that connectors conforming to the standard can be used on a wide range of products and peripherals and have been built into almost all new computers produced in the past several years.

Serial operation means that data is transferred in and out one bit (the basic unit of information in computing and digital communications) at a time, in contrast with parallel operation, which uses multiple wires (usually 16 or more) to transfer multiple bits simultaneously. A bus is a set of wires that provides electrical connections.

The trend for external busses is to employ a serial architecture. Parallel busses are much faster than serial busses for an identical clock speed (i.e., a rate in cycles per second at which a computer performs its most basic operations) because more bits are being transmitted simultaneously. However, it is considerably easier to increase the clock speed for a serial connection than for a parallel connection. This is in part because at high clock speeds parallel signals tend to interfere with each other.

Another disadvantage of parallel cables is that they cost more than serial cables due to the greater number of wires and the extra electromagnetic shielding that they require. Moreover, serial cables can be used for longer distances.

Plug-and-play, also called PnP and hot swapping, refers to the ability to connect new peripherals to a computer without having to restart it. Introduced on some operating systems from the early 1990s, it represented a major convenience for users.

Another advantage of USB is that it allows a single type of connector to replace a variety of types that were used for individual devices, thereby lowering costs for both product makers and users and eliminating the difficulty for unskilled computer users to find the correct socket for a certain type of connector. USB connectors can also be physically easier to insert and remove than some other types and are less vulnerable to damage (especially the accidental bending of individual pins).

In addition, individual devices can be daisy chained together (up to 127 devices) for added convenience. For example, the connector on a USB mouse or camera can be plugged directly into a socket on a USB keyboard (which is plugged into the computer or other USB device) instead of having to be plugged directly into the computer. Moreover, USB cables can accommodate sufficient power (5V) for several connected devices, thereby reducing or eliminating the need for separate power supply cables.

The first version of USB, USB 1.0, was introduced in 1995. It supports two data rates: 1.5 Mbps (megabits per second) for keyboards, mice, joysticks, etc. and a full speed mode at 12 Mbps. USB 2.0, introduced in 2002, features a speed of 40 times that of USB 1.0 at 480 Mbps while maintaining full backward compatibility with it. This allows USB 2.0 to compete directly with FireWire, except in the area of digital camcorders, where it is restrained by technical limitations. Developed in 1995 by Apple Computer, the newest version (Firewire 800) allows a maximum speed of 786.432Mbps.

Wireless USB is a new standard that uses the ultra-wide band (3.1 GHz to 10.6 GHz) to provide the same 480 Mbps data rate as USB 2.0 within two meters and 110 Mbps within ten meters while maintaining backward compatibility with both USB 1.1 and USB 2.0.

Created December 26, 2006.
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