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In USB 3.0, dual-bus architecture is used to allow both USB 2.0 (Full Speed, Low Speed, or High Speed) and USB 3.0 (SuperSpeed) operations to take place simultaneously, thus providing backward compatibility. The structural topology is the same, consisting of a tiered star topology with a root hub at level 0 and hubs at lower levels to provide ...
The physical phenomena on which the device relies (such as spinning platters in a hard drive) will also impose limits; for instance, no spinning platter shipping in 2009 saturates SATA revision 2.0 (3 Gbit/s), so moving from this 3 Gbit/s interface to USB 3.0 at 4.8 Gbit/s for one spinning drive will result in no increase in realized transfer rate.
The Hi-Speed USB logo. USB 2.0 was released in April 2000, adding a higher maximum signaling rate of 480 Mbit/s (maximum theoretical data throughput 53 MByte/s [25]) named High Speed or High Bandwidth, in addition to the USB 1.x Full Speed signaling rate of 12 Mbit/s (maximum theoretical data throughput 1.2 MByte/s). [26]
According to a USB-IF chairman, "at least 10 to 15 percent of the stated peak 60 MB/s (480 Mbit/s) of Hi-speed USB goes to overhead—the communication protocol between the card and the peripheral. Overhead is a component of all connectivity standards". [1] Tables illustrating the transfer limits are shown in Chapter 5 of the USB spec.
The xHCI reduces the need for periodic device polling by allowing a USB 3.0 or later device to notify the host controller when it has data available to read, and moves the management of polling USB 2.0 and 1.1 devices that use interrupt transactions from the CPU-driven USB driver to the USB host controller.
USB 2.0 provides for a maximum cable length of 5 metres (16 ft 5 in) for devices running at high speed (480 Mbit/s). The primary reason for this limit is the maximum allowed round-trip delay of about 1.5 μs. If USB host commands are unanswered by the USB device within the allowed time, the host considers the command lost.
USB 3.0 SuperSpeed and USB 2.0 High-Speed versions defined USB 3.0 SuperSpeed – host controller (xHCI) hardware support, no software overhead for out-of-order commands; USB 2.0 High-speed – enables command queuing in USB 2.0 drives; Streams were added to the USB 3.0 SuperSpeed protocol for supporting UAS out-of-order completions
The American Association of State Highway and Transportation Officials (AASHTO) is a standards setting body which publishes specifications, test protocols, and guidelines that are used in highway design and construction throughout the United States. Despite its name, the association represents not only highways but air, rail, water, and public ...