This document gives an overview of the USB Mass Storage Class specifications. How <em>mass</em> <em>storage</em> devices behaveon the USB bus is the subject of this and other USB Mass Storage Class specifications. At this time, four other USBMass Storage Class specifications are under development by the USB Mass Storage Class Working Group (CWG).The titles of these specifications are:USB Mass Storage Class Control/Bulk/Interrupt (CBI) TransportUSB Mass Storage Class Bulk-Only TransportUSB Mass Storage Class ATA Command BlockUSB Mass Storage Class UFI Command Specification
Universal Serial Bus Mass Storage ClassUFI Command SpecificationA UFI Device is a removable-media <em>mass</em> <em>storage</em> subsystem, which connects to a Host computer via itsUniversal Serial Bus (USB) port. The Host and UFI Device communicate by exchanging Command Blocks,data, and status information as defined by this specification. The method used to transport this information overthe USB is defined by the Bulk-Only or CBI transport specifications.A conceptual view of the Host and UFI Device is shown in Figure 1. The UFI device is represented by a USBFloppy Disk Unit (USB FDU). The UFI device driver software running on the Host controls the UFI device bysending it UFI command blocks defined by this specification. The UFI Function in the device processes thesecommand blocks as specified herein.All exchanges of command block, data, and status information are carried out by the transfer of packets over theUSB. This exchange is managed by the USB Driver on the Host, and the USB Logical Device process in theUSB-FDU.
Universal Serial Bus Mass Storage ClassBulk-Only TransportThis specification addresses Bulk-Only Transport, or in other words, transport of command, data, and statusoccurring solely via Bulk endpoints (not via Interrupt or Control endpoints). This specification only uses thedefault pipe to clear a STALL condition on the Bulk endpoints and to issue class-specific requests as definedbelow. This specification does not require the use of an Interrupt endpoint.This specification defines support for logical units that share common device characteristics. Although thisfeature provides the support necessary to allow like <em>mass</em> <em>storage</em> devices to share a common USB interfacedescriptor, it is not intended to be used to implement interface bridge devices.