* The non-serial nature of USB 3.0 makes these translations an inexact correlation, but an idea of the increase in transmission speeds can be seen through these estimations. The size of a service interval (125µs) represents the minimum theoretical rate of data transmission, or what would roughly equate to a 8000Hz polling rate in USB 2.0 terms*. A SuperSpeed interrupt can move up to three maximum sized packets per service interval (125µs, formerly known as a micro-frame), meaning that the maximum theoretical rate at which data can be received by the host is every 41.6µs, the equivalent of a 24000Hz polling rate in USB 2.0 terms*. This last note is of particular importance as each device now sends data when it is recorded it is still host controlled, but in a different way that no longer limits packet sizes. Also note that in the USB 3.0 specification continuous device polling has been eliminated and has been replaced by asynchronous notices. SuperSpeed USB also supports continuous bursting for all types of functional data transfers, unlike USB 2.0. SOP packets have been replaced by isochronous timestamp packets (ITPs), while token packets have also been removed (IN is replaced by the handshake packet, while OUT has been incorporated into the data packet). A few notable changes in dataflow should be mentioned.Ī dual simplex connection is now being used which allows packets to leave and arrive simultaneously these transfers are also no longer serial in nature (where packets must finish before the next begins). The basic data flow and transfer concepts are preserved, while some packets or specifications have been integrated or removed entirely. The USB 3.0 specification dramatically changes the way that a host and HID-devices communicate. A Special Note on Future USB Specifications

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