本国际标准定义了机械、电气、定时和协议要求 SCSI并行接口，允许符合要求的设备进行互操作。SCSI并行接口是本地的 可以在很宽的传输速率范围内操作的I/O总线。SCSI并行的目标 接口是 a)在一类设备内为主机提供设备独立性。因此，不同的磁盘 驱动器、磁带驱动器、打印机、光学介质驱动器和其他设备可以添加到主机 不需要修改通用系统硬件的计算机。拨备用于 通过使用供应商特定的选项添加特殊特性和功能。保留区 为将来的标准化提供。 b)提供兼容性，使得适当符合SCSI-2设备可以与 SCSI-3设备，前提是系统工程正确完成。正确符合SCSI-2标准 设备应以可接受的方式响应拒绝SCSI-3协议扩展。SCSI-3 协议扩展被设计成允许这种拒绝，因此允许SCSI-2 设备继续运行而不需要使用扩展。 接口协议包括提供多个启动器（能够 启动I/O进程）和多个目标（能够响应请求以执行 I/O进程）。分布式仲裁（即总线竞争逻辑）内置于SCSI的体系结构中。A 默认优先级系统将接口控制权授予争用的最高优先级SCSI设备 定义了总线的使用和可选的公平算法。 本标准定义了用于互连计算机的输入/输出总线的物理属性 外围设备。 图1旨在显示SCSI标准的一般结构。该图并不意味着 关系，如层次结构、协议栈或系统架构。 公共存取方法 图1-SCSI的一般结构 该国际标准旨在替代SCSI-3并行接口标准。这个 国际标准，除了包含SCSI-3并行接口标准中的所有信息 包含LVD和fast-40的信息和规格以及许多其他改进。

This international standard defines the mechanical, electrical, timing, and protocol requirements of the SCSI parallel interface to allow conforming devices to interoperate. The SCSI parallel interface is a local I/O bus that may be operated over a wide range of transfer rates. The objectives of the SCSI parallel interface are a) To provide host computers with device independence within a class of devices. Thus, different disk drives, tape drives, printers, optical media drives, and other devices may be added to the host computers without requiring modifications to generic system hardware. Provision is made for the addition of special features and functions through the use of vendor-specific options. Reserved areas are provided for future standardization. b) To provide compatibility such that properly conforming SCSI-2 devices may interoperate with SCSI-3 devices given that the systems engineering is correctly done. Properly conforming SCSI-2 devices should respond in an acceptable manner to reject SCSI-3 protocol extensions. SCSI-3 protocol extensions are designed to be permissive of such rejections and thus allow the SCSI-2 devices to continue operation without requiring the use of the extension. The interface protocol includes provision for the connection of multiple initiators (SCSI devices capable of initiating an I/O process) and multiple targets (SCSI devices capable of responding to a request to perform an I/O process). Distributed arbitration (i.e., bus-contention logic) is built into the architecture of SCSI. A default priority system awards interface control to the highest priority SCSI device that is contending for use of the bus and an optional fairness algorithm is defined. This standard defines the physical attributes of an input/output bus for interconnecting computers and peripheral devices. Figure 1 is intended to show the general structure of SCSI standards. The figure is not intended to imply a relationship such as a hierarchy, protocol stack, or system architecture. Common Access Method

Figure 1 - General Structure of SCSI This international standard is intended as an alternate to the SCSI-3 Parallel Interface Standard. This international standard, in addition to containing all the information in the SCSI-3 Parallel Interface Standard contains information and specifications for LVD and fast-40 along with many other improvements.