USB's main attraction is that it makes adding peripherals to your computer incredibly easy. It enables you to connect peripherals to the outside of the computer so you don't have to open your PC.
Introduced in 1995, the USB standard was developed by industry leaders including DEC®, IBM®, Intel®, Microsoft®, and Compaq®. Most PCs and peripherals available today feature at least one USB connection. Peripherals can include everything from modems to joysticks. Windows® 95 Rev. B, Windows 98, Windows 2000, Windows Me, and Mac® OS 8 and higher support USB.
A USB peripheral simply plugs right into the port and works. You don't need to install a card; you don't even need to turn off your computer—USB devices are completely hot-swappable. Because USB also distributes power, many USB devices don't require a separate power supply, although a bus-powered device must be attached upstream to either a host PC or a powered hub.
USB configuration happens automatically, so built-in USB means you don't have to fiddle with drivers and software when adding most peripherals. USB host controllers automatically detect when peripherals are connected to or disconnected from a port. The controllers manage and control the driver software and bandwidth required by each peripheral. They even allocate the right electrical power to each peripheral.
USB uses a tiered star topology, meaning that USB devices called hubs can serve as connection ports for other USB devices. Only one device needs to be actually plugged into your PC. USB supports hubs that can be either standalone or embedded within some other device such as a keyboard or disk drive. A single USB port can support up to 127 devices.
USB also improves the performance of joysticks and other game controllers. A common problem with traditional j
USB 1.1, the original USB standard, has two data rates: 12 Mbps for devices such as disk drives that need high-speed throughput and 1.5 Mbps for devices such as joysticks that need much lower bandwidth.
In 2002, a newer specification, USB 2.0, Hi-Speed USB 2.0, gained wide acceptance in the industry. It increases the speed of the peripheral-to-PC connection from 12 Mbps to 480 Mbps, or 40 times faster than USB 1.1. This increase in bandwidth enhances the use of external peripherals, such as CD/DVD burners, scanners, digital cameras, video equipment, that require high throughput. USB 2.0 also supports demanding applications where multiple high-speed devices run simultaneously, such as Web publishing. A USB 2.0 host will work with both USB 2.0 and USB 1.1 peripherals. USB 2.0 also supports Windows? XP through a Windows update.
An even newer USB standard, USB On-The-Go (USB OTG) is also being developed. USB OTG enables devices other than a PC to act as a host. Use it to connect portable equipment, such as PDAs, cell phones, and digital cameras, to each other without using a PC host.
There are four types of USB connectors: Type A, Type B, Mini B, and Mini A.
USB 1.1 specifies the Type A and Type B. USB 2.0 specifies the Type A, Type B, and Mini B. The Mini A connector was developed as part of the USB OTG specification and is used for smaller peripherals, such as mobile phones.