任何计算机系统中最重要的部分之一就是I/O。许多系统需要不同类型的I/O，具体取决于具体的应用。此外，在I/O设备类型、接口以及为支持它们而设计的LSI组件方面，系统设计师面临着跟上新技术的重大挑战。IEEE 959 I/O扩展总线旨在满足这些需求。使用此标准接口可以以简单、经济高效的方式添加或修改少量I/O。IEEE 959 I/O扩展总线的指定与处理器或板类型无关。 每个扩展接口最多可直接支持16个8位I/O端口。使用从处理器或FIFO设备可以获得增强的寻址能力。此外，每个扩展接口可以可选地支持一个DMA信道，该信道的数据速率最高可达2 16位MWord/sec。8位和16位数据路径都支持这些功能。本规范是为那些打算设计或评估与IEEE 959输入/输出扩展总线兼容的产品的用户编写的。为此，详细介绍了功能、电气和机械规范。 本规范旨在保证基板和扩展模块之间的兼容性，同时不限制实际设计。附录中给出了不属于实际规范一部分的其他设计注意事项。

One of the most important parts of any computer system is the I/O. Many systems require different types of I/O depending on the specific application. In addition, the system designer is faced with a significant challenge to keep up with new technology in I/O devices types, interfaces, and the LSI components designed to support them. The IEEE 959 I/O expansion bus is designed to address these needs. Using this standard interface allows small increments of I/O to be added or modified in an easy, cost-effective way. The IEEE 959 I/O expansion bus is specified independent of processor or board type. Each expansion interface supports up to sixteen 8-bit I/O ports directly. Enhanced addressing capability is available using slave processors or FIFO devices. In addition, each expansion interface may optionally support a DMA channel capable of data rates up to 2 16-bit Mwords/sec. These features are supported for both 8- and 16-bit data paths. This specification has been prepared for those users who intend to design or evaluate products that will be compatible with the IEEE 959 I/O expansion bus. For this purpose, functional, electrical, and mechanical specification are covered in detail. The intent of the specification is to guarantee compatibility between baseboards and expansion modules while not restricting the actual designs any more than necessary. Additional design considerations that are not part of the actual specification are presented in the appendixes.