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The Massbus is a high-performance computer input/output bus designed in the 1970s by the Digital Equipment Corporation of Maynard, Massachusetts. The bus was used by Digital to interconnect its highest-performance computers with magnetic disk and magnetic tape storage equipment. The use of a common bus allowed the PDP-10, PDP-11, and VAX computer families to share a common set of peripherals. An additional business objective was to provide a subsystem entry price well below that of IBM storage subsystems which used large and expensive controllers unique to each storage technology and optimized for connecting large numbers of storage devices. ==Logical implementation== The bus is logically implemented as two separate sections: * An asynchronous control bus used to access memory-mapped I/O registers in the individual storage devices, and * A high-speed, synchronous data bus that is used to carry the actual data transfers between the storage devices and the host bus adapter. The data bus is 18 bits wide plus parity. 16 bits was used for PDP-11 and VAX systems, 18 bits for DEC-10s. * Multiple devices of different types can transmit data over the shared data path. However, this was never supported by DEC operating systems. * Static dual port is also provided to permit failover or manual switching of storage devices to another CPU. Massbus storage devices each contain their own autonomous controller units, allowing fully overlapped operation of multiple storage units connected to a single Massbus. The interface between the computer and the Massbus is basically a pass-through device that allows connection of the common Massbus to the individual computer's internal buses (whether PDP-10 memory bus, Unibus, PDP-11/70 cache bus, or VAX Synchronous Backplane Interconnect). Whenever a storage controller has a data transfer ready, it arbitrates for the use of the Massbus's synchronous data channel. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Massbus」の詳細全文を読む スポンサード リンク
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