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USB - Review (Basic Principles Of Work)
By admin | April 21, 2007
The need for a medium-speed, inexpensive plug and play interface that can be used to attach a practically unlimited number of devices was eventually recognised, and the solution was the Universal Serial Bus (USB). Universal Serial Bus (USB) is a serial bus standard to interface devices. It was designed for computers such as PCs and the Apple Macintosh, but its popularity has prompted it to also become commonplace on video game consoles, PDAs, cellphones; and even devices such as televisions and home stereo equipment (e.g., mp3 players), and portable memory devices. Devices that don’t require a lot of power can actually draw their power via the USB connection. High-powered devices have their own power supplies. You can connect up to 127 USB devices to your computer AND hot swap them. That means you can connect and disconnect them without having to reboot your computer. The radio spectrum-based USB implementation is known as Wireless USB.
Universal Serial Bus (from now on referred to as “USB”) was devised as a key component in the trajectory towards a legacy-free PC, i.e. the idea was to let go of all older serial and parallel ports on personal computers since these were not properly standardized, and required a multitude of device drivers to be developed and maintained.
The USB was designed to allow large numbers (up to 127) of low- and medium-speed peripherals to be attached to a PC. With a top transfer rate of 12Mbit/sec USB was never intended to be an alternative to SCSI. But it is still much faster than the serial or parallel ports.
A USB system has an asymmetric design, consisting of a host controller and multiple daisy-chained devices. Additional USB hubs may be included in the chain, allowing branching into a tree structure, subject to a limit of 5 levels of branching per controller. No more than 127 devices, including the bus devices, may be connected to a single host controller. Modern computers often have several host controllers, allowing a very large number of USB devices to be connected. USB cables do not need to be terminated.
However, for economical and technical reasons, daisy chaining never became widespread. To reduce the necessity of USB hubs, computers now come with a large number of USB ports, typically six.
Particular attention was paid to the needs of audio and video devices, which it was envisaged would be increasingly important for the next generation of personal productivity applications. The design of the USB provides for this time-critical isochronous data to be delivered without delays that would adversely affect the quality of images and speech.
USB can connect peripherals such as mouse devices, keyboards, gamepads and joysticks, scanners, digital cameras, printers, external storage, networking components, etc. For many devices such as scanners and digital cameras, USB has become the standard connection method. USB is also used extensively to connect non-networked printers, replacing the parallel ports which were widely used; USB simplifies connecting several printers to one computer. As of 2005, the only large classes of peripherals that cannot use USB, because they need a higher data rate than USB can provide, are displays and monitors, and high-quality digital video components.
USB was designed to be plug and play. Devices can be added and removed even while the system is running, avoiding the need to reboot the system to reconfigure it. Technical issues like bus termination and the assignment of device identifiers are taken care of by the hardware and software architecture so these common sources of configuration error will not be a problem. Concerns for power conservation have been catered for by allowing devices to be suspended and resumed.
Typical USB devices are those requiring low and medium bandwidths. At the bottom end of the bandwidth range, USB could be used to connect a keyboard and mouse to a PC. At the top end, scanners, backup devices or cameras for video-conferencing applications could use USB, eliminating the need for proprietary interface boards with their associated installation and configuration problems.
Sources: http://en.wikipedia.org/wiki/Usb, http://www.tech-pro.net/intro_usb.html,
http://www.pcmech.com/show/internal/681/
Topics: Computers & Software |