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[[File:Locale_RS6_Sun SuperSPARC II SM71 501-3001.jpg|thumb|right|MBus module, Sun SuperSPARC II SM71]]
[[File:Mbus_mit_modul.jpg|thumb|right|Two MBus connectors (top of photograph), one occupied by CPU module]]
[[File:Locale_RS6_Mbus male connector cropped.jpg |thumb |upright=2.0 |right|MBus male connector]]
'''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]]. [[SBus]] is used in the same machines to connect add-on cards to the motherboard.

MBus was first used in Sun's first [[multiprocessor]] [[SPARC]]-based system, the [[SPARCserver]] 600MP series (launched in 1991), and later found use in the [[SPARCstation 10]] and [[SPARCstation 20]] workstations. The bus permits the integration of several microprocessors on a single motherboard, in a [[multiprocessing]] configuration with up to eight [[CPU]]s packaged in detachable MBus modules. In practice, the number of processors per MBus is limited to four. Single processor systems were also sold that use the MBus protocol internally, but with the CPUs permanently attached to the motherboard to lower manufacturing costs.

MBus specifies a [[64-bit]] [[datapath]], which uses [[36-bit]] [[physical address]]ing, giving an [[address space]] of 64 [[gigabyte|GB]]. The transfer rate is 80 [[megabyte|MB]]/s sustained (320 MB/s peak) at 40 MHz, or 100 MB/s (400 MB/s peak) at 50 MHz. Bus controlling is done by an [[arbiter (electronics)|arbiter]]. Interrupt, reset, and timeout logic are also specified.

== Related buses ==
Several related buses were also developed:


=== XBus ===
XBus is a packet-switched bus used in the SPARCserver 1000, SPARCcenter 2000 and [[Cray CS6400]]. This corresponds to the circuit-switched MBus, with identical electrical characteristics and physical form factor but an incompatible signalling protocol.


=== KBus ===
KBus is a high-speed interconnection system for linking multiple MBuses, used in [[Solbourne Computer]] Series 6 and Series 7 computer systems.

== History ==

The MBus standard was cooperatively developed by Sun and [[Ross Technology]] and released in 1991.<ref>[http://www.thefreelibrary.com/hyperSPARC+GOES+HOLLYWOOD%3b+PIXAR+USES+hyperSPARC+MICROPROCESSORS+FROM...-a017824466 "HyperSPARC goes Hollywood; Pixar uses HyperSPARC microprocessors from Ross Technology to create final rendering of 'Toy Story'"] {{Webarchive|url=https://web.archive.org/web/20121020184245/http://www.thefreelibrary.com/hyperSPARC+GOES+HOLLYWOOD%3b+PIXAR+USES+hyperSPARC+MICROPROCESSORS+FROM...-a017824466 |date=2012-10-20 }}.</ref>

Manufacturers who produced computer systems using the MBus included Sun, Ross Technology, [[Hyundai Group|Hyundai]]/[[Axil Computer|Axil]], [[Fujitsu]], [[Solbourne Computer]], [[Tatung Company|Tatung]], GCS, [[Auspex Systems|Auspex]], [[ITRI]], [[International Computers Limited|ICL]], [[Cray]], [[Amdahl Corporation|Amdahl]], [[Themis Computer|Themis]], [[DTK Computer|DTK]] and Kamstrup.

==See also==
*[[List of interface bit rates]]

== References ==
<references />

==External links==
* [http://mbus.sunhelp.org/ ''The Rough Guide to MBus Modules'', sunhelp.org]
* [https://web.archive.org/web/20000815231207/http://www.sparc.com/standards/MBUS.ps.Z MBus Specification]

{{Computer bus}}
{{Sun Microsystems}}

[[Category:Computer buses]]
[[Category:Sun Microsystems hardware]]
[[Category:Computer-related introductions in 1991]]

MBus (SPARC) - Revision history

RS-485: Imported from Wikipedia (overwrite)