Universal Serial Bus (USB) is a bus standard that was originally specified in 1995. The major goal of USB is to define an expansion bus that makes it easy to add peripherals to a PC. Today all new PCs come with one or more USB ports. This has been enabled by the "Easy PC Initiative" being led by Microsoft and Intel, which is an effort to provide consumers with simpler, easier-to-use PCs that do not sacrifice connectivity or expandability - and USB provides exactly this. USB also allows hot swapping of devices on a home network, without the need of shutting down and restarting devices.

USB is playing a key role in fast-growing consumer areas: digital imaging, PC telephony, and multimedia games. The presence of USB in most new PCs, and its plug-and-play capability, means that PCs and peripherals  (such as CD ROM drives, tape and floppy drives, scanners, printers, video devices, digital cameras, digital speakers, telephones, modems, keyboards, mice, digital joysticks and others) will automatically configure and work together, with a high degree of reliability, in these exciting new application areas. USB distributes power to all connected devices and allows bi-directional data transfer, making it a natural choice for connecting information appliances across the home. USB opens the door to new levels of innovation and ease of use for input devices, such as the new generation of "force-feedback" digital joysticks. There are also brand new opportunities for all types of peripherals from printers to scanners to high speed connections such as Ethernet, DSL, cable, and satellite communications.

Introduction to USB 1.1

USB version 1.1 has gained tremendous success in the marketplace, with most PC and peripheral vendors worldwide developing products based on this specification. 

USB supports two high-speed data transfer protocols: isochronous and asynchronous. Isochronous connections from the PC USB port to the peripherals such as scanners, video devices, digital cameras and printers, supports data transfers at a guaranteed, fixed rate of delivery of 12 Mbps. The slower asynchronous protocol is used to communicate with peripherals such as keyboards and mice at 1.5 Mbps.

These data rates of up to 12 Mbps are sufficient for low-speed to medium-speed peripherals. It replaces many different serial and parallel connectors at the back of the PC with one standardized plug-and-play combination, and home networking devices with a USB port can connect up to 127 different USB peripherals. USB's data rate also accommodates a whole new generation of peripherals, including MPEG-2 video-based products, data gloves, and digitizers. Computer-telephony integration is expected to be a big growth area for PCs, and USB can provide an interface for ISDN and digital PBXs.

Introduction to USB 2.0

USB 2.0, is mostly like USB 1.1, but the next generation specification extends the bandwidth and hence increases the connection speeds between the PCs and the peripherals. USB 2.0 has over 40 times the data rate as USB 1.1 increasing data rates from 12 Mbps to 480 Mbps respectively, and hence extending its capabilities. 

The higher bandwidth will support the most demanding PC applications, such as digital image creation and Web publishing, where multiple high-speed peripherals will be running simultaneously. This enables USB to potentially offer a complete home networking interconnectivity solution.