This standard defines a circular queue interface for transferring information between a PQI host and a PQI device over the PCI Express architecture, and defines a scatter gather list (SGL) format that is used to describe data buffers. The SCSI family of standards provides for many different transport protocols that define the rules for exchanging information between different SCSI devices. This standard defines the rules for exchanging information between SCSI devices using a PCI Express queuing layer. Other SCSI transport protocol standards define the rules for exchanging information between SCSI devices using other interconnects. PCI Express is used as the interconnect for this standard. This standard defines a generic queuing model to allow transporting IUs.