UAS_BOT区别.docx

Whats the Difference Between USB UASP And BOTUSB 3.0 offers approximately 10:1 performance improvement over USB 2.0, but realizing the full potential of that gain for mass storage devices poses additional challenges. The mainstay of mass storage standards for USB 2.0 and 1.1 has been the Bulk Only Transport (BOT) device class specification for USB, and it has served the personal computer industry well with its simplicity and modest efficiency. It has proven to be simple and inexpensive to implement in microprocessor-based systems, including personal computers, and hence suitable for inexpensive flash-based mass storage devices.In Bulk Only Transport, standard USB Bulk transactions are used for each stage of a mass storage transfer - command, data, and status. In fact, early versions of the BOT standard referred to it as BBB, short for Bulk/Bulk/Bulk, which was an enhancement over the older Control/Bulk/Interrupt (CBI) standard that was used (and still is) mainly for full-speed USB floppy disk drives.Higher performance mass storage devices tend to use the SCSI standards (Small Computer System Interface), which allow devices to support performance-enhancing modes of operation such as multiple outstanding requests and out-of-order request completions. Multiple outstanding requests mean that the system doesnt need to wait for each request to be completed before the next request can be sent to the device. The device simply stores the requests in its own buffer, sends a completion back to the host as each request is completed, and starts working on the next request in the buffer as soon as the previous one is completed. This allows the device to be more fully utilized if the USB link can keep up with the additional bus traffic, as USB 3.0 finally can.But the original BOT standard had no provision for supporting multiple outstanding requests. A new USB standard was needed, and with USB 3.0 there has been a new industry initiative to provide an improved mass storage class s