Universal Serial Bus (USB) is an industry standard developed in the mid-1990s that defines the cables, connectors and communications protocols used in a bus for connection, communication and power supply between computers and electronic devices. Also known as Hi-Speed USB, USB 2.0 is an external bus that supports data rates up to 480Mbps. USB 2.0 is an extension of USB 1.1. USB 2.0 is fully compatible with USB 1.1 and uses the same cables and connectors.
The USB 2.0 specification was released in April 2000 and was ratified by the USB Implementers Forum (USB-IF) at the end of 2001. Hewlett-Packard, Intel, Lucent Technologies, NEC and Philips jointly led the initiative to develop a higher data transfer rate, with the resulting specification achieving 480 Mbit/s, a fortyfold increase over the original USB 1.1 specification.
USB 2.0 has full forward and backward compatibility with original USB devices and works with cables and connectors made for original USB, too. USB 2.0 supports low-bandwidth devices such as keyboards and mice, as well as high-bandwidth ones like high-resolution webcams, scanners, printers and high-capacity storage systems. The deployment of USB 2.0 allowed PC industry leaders to forge ahead with the development of PC peripherals to complement existing high-performance PCs. In addition to improving functionality and encouraging innovation, USB 2.0 increases the productivity of user applications and allows the user to run multiple PC applications at once or several high-performance peripherals simultaneously.
USB 1.1 allowed a maximum transfer rate of 12Mbits/second. It is now obsolete, but both of its speeds (1.5Mbps & 12Mbps) are being adopted into USB 2.0, and they are now called Original USB officially. Almost every conceivable peripheral has USB 2.0 version ranging from a HDTV tuner, surround gaming headset, portable hard drive to even USB video card.Should you own a laptop, you may like to know that USB is also your ticket out of the proprietary world. It used to be that docking stations must all match that exact notebook model due to the proprietary connection. Now, you can just plug in a USB notebook dock, and you’ll get a USB video adapter, hub, 7.1 surround audio, serial converters, Ethernet plus a notebook holder.
The host controller directs traffic flow to devices, so no USB device can transfer any data on the bus without an explicit request from the host controller. In USB 2.0, the host controller polls the bus for traffic, usually in a round-robin fashion. The throughput of each USB port is determined by the slower speed of either the USB port or the USB device connected to the port.
High-speed USB 2.0 hubs contain devices called transaction translators that convert between high-speed USB 2.0 buses and full and low speed buses. When a high-speed USB 2.0 hub is plugged into a high-speed USB host or hub, it will operate in high-speed mode. The USB hub will then either use one transaction translator per hub to create a full/low-speed bus that is routed to all full and low speed devices on the hub, or will use one transaction translator per port to create an isolated full/low-speed bus per port on the hub.
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