The set of SCSI (Small Computer System Interface) standards consists of this standard and the SCSI implementation standards described in the precedence requirements (see 1.2). This standard defines a reference model that specifies common behaviors for SCSI devices and an abstract structure that is generic to all SCSI I/O system implementations. The set of SCSI standards specifies the interfaces, functions and operations necessary to ensure interoperability between conforming SCSI implementations. This part of ISO/IEC 14776 is a functional description. Conforming implementations may employ any design technique that does not violate interoperability. The following architecture model concepts from previous versions of this standard are made obsolete by this edition: a) support for the SPI-5 SCSI transport protocol (except for informational listings in Annex A); b) contingent allegiance; c) the TARGET RESET task management function and d) untagged tasks.