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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 Linux kernel mainline contains support for USB 3.0 since version 2.6.31, which was released in September 2009. [32] [33] [34] FreeBSD supports USB 3.0 since version 8.2, which was released in February 2011. [35] Windows 8 was the first Microsoft operating system to offer built in support for USB 3.0. [36]
USB ports and connectors are often color-coded to distinguish their different functions and USB versions. These colors are not part of the USB specification and can vary between manufacturers; for example, the USB 3.0 specification mandates appropriate color-coding while it only recommends blue inserts for Standard-A USB 3.0 connectors and plugs.
The most significant technical differences between FireWire and USB include: USB networks use a tiered-star topology, while IEEE 1394 networks use a tree topology. USB 1.0, 1.1, and 2.0 use a "speak-when-spoken-to" protocol, meaning that each peripheral communicates with the host when the host specifically requests communication.
Any USB 2.0 hub that supports a higher standard than USB 1.1 (12 Mbit/s) will translate between the lower standard and the higher standard using what is called a transaction translator (TT). For example, if a USB 1.1 device is connected to a port on a USB 2.0 hub, then the TT would automatically recognize and translate the USB 1.1 signals to ...
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
Formally, a cable type and properties are defined by a distinct specification version, which was used during the development/design of said cable model, so each cable would be a valid and possibly certified cable according to a specific set of USB specification versions, like "Type-C 2.3, USB 3.2, USB4 Version 2.0".
z Uses 8b/10b encoding, meaning that 20% of each transfer is used by the interface instead of carrying data from between the hardware components at each end of the interface. For example, a single link PCIe 1.0 has a 2.5 Gbit/s transfer rate, yet its usable bandwidth is only 2 Gbit/s (250 MB/s).