USB Attached SCSI is a computer protocol used to move data to and from USB storage devices such as hard drives, solid-state drive

Solid-state drive

A solid-state drive , sometimes called a solid-state disk or electronic disk, is a data storage device that uses solid-state memory to store persistent data with the intention of providing access in the same manner of a traditional block i/o hard disk drive...

s, and thumb drives. UAS depends on the USB protocol, and uses the standard SCSI

SCSI

Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it...

 command set.
UAS is defined across two standards, the T10 "USB Attached SCSI" (T10/2095-D) referred to as the "UAS" specification, and the USB "Universal Serial Bus Mass Storage Class - USB Attached SCSI Protocol (UASP)" specification.
The T10 technical committee of the International Committee for Information Technology Standards (INCITS) develops and maintains the UAS specification; the SCSI Trade Association

SCSI Trade Association

The SCSI Trade Association, or SCSITA, is an industry trade group which exists to promote the use of SCSI technology. It was formed in 1996. , sponsor members include HP, Intel, LSI Logic, and Seagate...

 (SCSITA) promotes the UAS technology.
The USB mass-storage device class (MSC) Working Group develops and maintains the UASP specification; the USB Implementers Forum

USB Implementers Forum

The USB Implementers Forum is a non-profit organisation to promote and support the Universal Serial Bus. Its main activities are the promotion and marketing of USB, Wireless USB, USB On-The-Go, and the maintenance of the specifications, as well as a compliance program.It was formed in 1995 by the...

, Inc. (USB-IF) promotes the UASP technology.

UAS Goals

• Designed to directly address the failings of the USB mass-storage device class Bulk-Only Transports (BOT)
  • Enables Command Queuing and out-of-order completions for USB mass-storage devices
  • Eliminates software overhead for SCSI command phases
• Up to 64K commands may be queued
• SCSI SAM-4 compliant
• USB 3.0 SuperSpeed and USB 2.0 High-speed versions defined
  • USB 3.0 SuperSpeed – host controller hardware support, no software overhead for out-of-order commands
  • USB 2.0 High-speed – Significantly 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
  • USB 3 host controller (xHCI) provides hardware support for Streams