New IEEE Standard - Inactive-Withdrawn. Withdrawn Standard. Specifications for the subsystem bus of the IEC 821 BUS, referred to as the VSB, are set forth. VSB is a local subsystem extension bus that allows a processor board to access additional memory and I/O over a local bus, removing traffic from the global bus and improving the total throughput of the system. The objectives are: to improve the performance of multiprocessor systems by allowing the design of local subsystems; to specify the electrical characteristics required to design boards that will reliably transfer data over the VSB; to specify the mechanical requirements to be compatible with VSB systems; to specify protocols that precisely define the interaction between the VSB and devices interfaced to it; and to provide terminology and definitions that describe VSB protocols.