Withdrawn Standard. Withdrawn Date: Mar 06, 2000. No longer endorsed by the IEEE. A simple, high-performance (37.5 Mbyte/s) backplane bus that provides the functions required by multiprocessor systems is defined. NuBus is a synchronous (10 MHz), multiplexed, multimaster bus that provides a fair arbitration mechanism. The logical, electrical, and physical interface standard for circuit boards that allows them to connect to and communicate over a backplane, as well as the backplane environment that must be provided to these boards, is described and specified. The protocol specification covers signal determinacy, bus cycles, transactions, block transfers, attention cycles, arbitration, address space, and utility functions. The physical specification covers timing, dc and ac specifications for signals, backplane (signal) characteristics, voltage and mechanical specifications for triple-height modules. Compliance requirements are stated. Concepts required for a general understanding of the NuBus specification, covering bus lines and bus operation, are included. This document also contains ANSI/IEEE Std 1101-1987, IEEE Standard for Mechanical Core Specifications for Microcomputers.