MBus
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MBus is a computer bus designed and implemented by Sun Microsystems for communication between high speed computer system components, such as the central processing unit, motherboard and main memory. Contrast this with SBus, used in the same machines to connect add-on cards to the motherboard.
MBus was first used in the initial SPARC-based multiprocessing system, the SPARCserver-690, and found use in several SPARC-based computer workstations (such as the SPARCstation series) beginning in the late 1980s. The bus permitted the integration of several microprocessors on a single motherboard, in a multiprocessing configuration with up to 8 CPUs with the CPUs were packaged in detachable MBus modules (see, for example, the SPARCstation 10 and SPARCstation 20). Single processor systems were also sold that used the MBus protocol internally, but had CPUs that were permanently attached to the motherboard to lower manufacturing costs.
MBus specified a 64-bit datapath, which used 36-bit physical addressing, giving an addess space of 64 GByte. The transfer rate is 80 MByte/s (320 MByte/s peak). Bus controlling is done by an Arbiter. Interrupt, reset, and timeout logic are also specified.
Several related buses were also developed, such as XBus, a packet-switched bus corresponding to the circuit-switched MBus, with identical electrical characteristics and physical form factor but an incompatible signalling protocol, and KBus, a high-speed interconnection system for linking multiple MBuses, used in Solbourne Series 6 and Series 7 computer systems.
Among the computer system manufacturers who produced computer systems using the MBus were Sun Microsystems, Ross Technology, Inc., Hyundai/Axil, Fujitsu, Solbourne, Tatung, GCS, Auspex, ITRI, ICL, Cray, Amdahl, Themis and DTK.
