Multibus is a computer bus standard used in industrial systems. It was developed by Intel Corporation and was adopted as the IEEE 796 bus.[1]

The Multibus specification was important because it was a robust, well-thought out industry standard with a relatively large form factor, so complex devices could be designed on it. Because it was a well-defined and well-documented industry standard, it allowed a Multibus-compatible industry to grow around it, with many companies making card cages and enclosures for it. Many others made CPU, memory, and other peripheral boards. In 1982 there were over 100 Multibus board and systems manufacturers.[2] This allowed complex systems to be built from commercial off-the-shelf hardware, and also allowed companies to innovate by designing a proprietary Multibus board and then integrating it with other vendors' hardware to create a system. A good example of this was Sun Microsystems with their Sun-1 and Sun-2 workstations. Sun built custom-designed CPU, memory, SCSI, and video display boards, and then added 3Com Ethernet networking boards, Xylogics SMD disk controllers, Ciprico Tapemaster 1/2 inch tape controllers, Sky Floating Point Processor, and Systech 16-port Terminal Interfaces in order to configure the system as a workstation or a file server.[3] Other workstation vendors who used Multibus-based designs included HP/Apollo[4] and Silicon Graphics IRIS.[5]

The Intel Multibus I & II product line was purchased from Intel by RadiSys Corporation, which in 2002 was then purchased by U.S. Technologies, Inc.

Intel iSBC 386 116 Multibus II Single Bus Computer
Intel iSBC 386/116 Multibus II Single Board Computer with VLSI A82389 as Multibus Controller.

Multibus architecture

Multibus is an asynchronous bus that accommodates devices with various transfer rates while maintaining maximum throughput. It had 20 address lines so it could address up to 1 Mb of Multibus memory and 1 Mb of I/O locations. Most Multibus I/O devices only decoded the first 64 Kb of address space.

Multibus supported multi-master functionality that allowed it to share the Multibus with multiple processors and other DMA devices.[6]

The standard Multibus form factor was a 12-inch-wide (300 mm), 6.75-inch-deep (171 mm) circuit board with two ejection levers on the front edge. The board had two buses. The wider P1 bus which pin assignment was defined by the Multibus specification. A second smaller P2 bus was also defined as a private bus.

Multibus standards

Multibus includes the following buses:

  • Multibus System Bus — adopted as IEEE 796
  • iSBX (I/O Expansion Bus) — adopted as IEEE P959
  • iLBX Local Bus Extension[7] (Execution Bus)
  • Multichannel I/O Bus


Multibus I

IEEE-796: Microcomputer System Bus; First released by Intel in 1974. The cards did not use front panels, and they used card edge fingers as the connectors (similar to ISA/PC-AT cards). Companies like Northwest Technical still provide "End of Life" products for Multibus I. This bus is obsolete.

  • IEC 796-1:1990 Microprocessor system bus—8-bit and 16-bit data (Multibus I) — Part 1: Functional description with electrical and timing specifications
  • IEC 796-2:1990 Microprocessor system bus—8-bit and 16-bit data (Multibus I) — Part 2: Mechanical and pin descriptions for the system bus configuration, with edge connectors (direct)
  • IEC 796-3:1990 Microprocessor system BUS I, 8-bit and 16-bit data (Multibus I) — Part 3: Mechanical and pin descriptions for the Eurocard configuration with pin and socket (indirect) connectors

Multibus II

IEEE-1296 32-bit/10 MHz bus, at 40 Mbyte/s. Card sizes are 3U x 220 mm, and 6U x 220 mm. These cards are larger than the VME Eurocard sizes, which are 3U/6U x 160mm. It uses TTL ("Fast" series) gates for drivers and the Backplane Connectors are DIN 41612 type C. Multibus II is not yet considered obsolete, but considered mature; however it is not recommended for new designs. IEEE-STD-1296: High-performance synchronous 32-bit bus: Multibus II, released in 1987, and 1994. Also as ISO/IEC 10861.

  • ISO/IEC 10861:1994 Information technology—Microprocessor systems—High-performance synchronous 32-bit bus: Multibus II

Historical uses

Multibus-II hardware running the iRMX operating system is used in the majority of the core Automatic Train Supervision subsystems on CLSCS, the London Underground Central line Signals Control System. This was supplied by Westinghouse Rail Systems and commissioned from the mid-1990s. The Central line is an Automatic Train Operation line. The Automatic Train Supervision elements use a mixture of iRMX on Multibus, and Solaris on SPARC computers. Sixteen Multibus-based Local Site Computers are distributed along the line together with six central Multibus-based subsystems in the control centre. Real time control and communications functions are provided by the Multibus-based processors and Sun workstations provide database functions and the operator consoles in the control room. All subsystem computers are dual redundant. The safety-critical Automatic Train Protection component is provided by trackside and train-borne equipment that does not use Multibus. The system was still in full operation as of 2011. In the control centre, Westinghouse also provided a cut-down mimic of the system for staff training and software test purposes using much of the same hardware and software as the full ATS system, but connected to a computer (also Multibus-II and Sun based) to simulate train movements and signalling behaviour.

Oslo Metro or Oslo Tunnelbane uses a similar, although less complex Westinghouse-supplied Multibus hardware control system through the central Common Tunnel or Fellestunnelen tracks, but was expected to be decommissioned in 2011.

See also


  1. ^ "IEEE Standard Microcomputer System Bus". Retrieved 2011-11-21.
  2. ^ The SUN Workstation Architecture, Andreas Bechtolsheim, Forest Baskett, Vaughan Pratt, Stanford University Computer systems Laboratory Technical Report No. 229, March 1982
  3. ^ The Sun Hardware Reference Archived January 2, 2007, at the Wayback Machine
  4. ^ "Archived copy". Archived from the original on 2010-06-08. Retrieved 2008-04-25.CS1 maint: Archived copy as title (link) HP/APOLLO SYSTEMS INFORMATION
  5. ^ Silicon Graphics IRIS 2000/3000 FAQ
  6. ^ Sun 68000 Board User's Manual, Sun Microsystems, Inc, February 1983, Revision B
  7. ^ AFIPS '83 Proceedings of the May 16-19, 1983, national computer conference, Pages 497-501. ACM digital library

External links

Alliant Computer Systems

Alliant Computer Systems was a computer company that designed and manufactured parallel computing systems. Together with Pyramid Technology and Sequent Computer Systems, Alliant's machines pioneered the symmetric multiprocessing market. One of the more successful companies in the group, over 650 Alliant systems were produced over their lifetime. The company was hit by a series of financial problems and went bankrupt in 1992.


A bus (contracted from omnibus, with variants multibus, motorbus, autobus, etc.) is a road vehicle designed to carry many passengers. Buses can have a capacity as high as 300 passengers. The most common type of bus is the single-deck rigid bus, with larger loads carried by double-decker and articulated buses, and smaller loads carried by midibuses and minibuses; coaches are used for longer-distance services. Many types of buses, such as city transit buses and inter-city coaches, charge a fare. Other types, such as elementary or secondary school buses or shuttle buses within a post-secondary education campus do not charge a fare. In many jurisdictions, bus drivers require a special licence above and beyond a regular driver's licence.

Buses may be used for scheduled bus transport, scheduled coach transport, school transport, private hire, or tourism; promotional buses may be used for political campaigns and others are privately operated for a wide range of purposes, including rock and pop band tour vehicles.

Horse-drawn buses were used from the 1820s, followed by steam buses in the 1830s, and electric trolleybuses in 1882. The first internal combustion engine buses, or motor buses, were used in 1895. Recently, interest has been growing in hybrid electric buses, fuel cell buses, and electric buses, as well as ones powered by compressed natural gas or biodiesel. As of the 2010s, bus manufacturing is increasingly globalised, with the same designs appearing around the world.

Bus (computing)

In computer architecture, a bus (a contraction of the Latin omnibus) is a communication system that transfers data between components inside a computer, or between computers. This expression covers all related hardware components (wire, optical fiber, etc.) and software, including communication protocols.Early computer buses were parallel electrical wires with multiple hardware connections, but the term is now used for any physical arrangement that provides the same logical function as a parallel electrical bus. Modern computer buses can use both parallel and bit serial connections, and can be wired in either a multidrop (electrical parallel) or daisy chain topology, or connected by switched hubs, as in the case of USB.

Callan Data Systems

Callan Data Systems, Inc. was an American computer manufacturer founded by David Callan in Westlake Village, California on January 24, 1980. The company was best known for their Unistar range of Unix workstations, and shut down again in 1985.

DIN 41612

DIN 41612 is a DIN standard for electrical connectors that are widely used in rack based electrical systems. Standardisation of the connectors is a pre-requisite for open systems, where users expect components from different suppliers to operate together. The most widely known use of DIN 41612 connectors is in the VMEbus system. They were also used by NuBus. The standard has subsequently been upgraded to international standards IEC 60603-2 and EN 60603-2.

DIN 41612 connectors are used in STEbus,Futurebus, VMEbus, Multibus II, NuBus, VXI Bus,

eurocard TRAM motherboards,

and Europe Card Bus,

all of which typically use male DIN 41612 connectors on Eurocards plugged into female DIN 41612 on the backplane in a 19-inch rack chassis.

Datacube Inc.

Datacube Inc. (1978–2005) was an image processing company that developed real-time hardware and software products for the industrial, medical, military and scientific markets.


Excelan was a computer networking company founded in 1982 by Kanwal Rekhi, Inder Singh and Navindra Jain. Excelan was a manufacturer of smart Ethernet cards, until the company merged with, and was acquired by Novell in 1989. The company offered a line of Ethernet "front end processor" boards for Multibus, VMEbus, Q-Bus, Unibus, and IBM AT Bus systems. The cards were equipped with their own processor and memory, and ran TCP/IP protocol software that was downloaded onto the cards from the host system. Excelan offered software like LAN Workplace that integrated the cards into a variety of operating system environments, including many flavors of UNIX, RSX-11, VMS, and DOS. The hardware and software were sold under the "EXOS" brand. In 1987, Excelan also acquired Kinetics, a small networking company that manufactured and sold a variety of Ethernet networking products for Apple Macintosh environments, most notably an AppleTalk-to-Ethernet gateway called the FastPath.

Excelan also manufactured and sold Ethernet network analyzer products, the first being the Excelan Nutcracker, followed later by the Excelan LANalyzer.


The Kinetics FastPath was a MacIP to TCP/IP router created in 1985 to allow Apple Macintosh computers (which at the time only had LocalTalk network connections) to communicate with other computers on Ethernet networks. The product had five significant revisions (known as KFPS-1 through KFPS-5) during its lifetime and was sold by Shiva Networks late in its existence. The FastPath itself was modeled after an implementation of the Stanford Ethernet - AppleTalk Gateway (SEAGATE) created at Stanford University Medical Center by Bill Croft in 1984 and 1985. SEAGATE was a combination of hardware and software that picked up IP packets from the Ethernet network and encapsulated them inside of DDP packets on the AppleTalk network and conversely picked up specially-encoded DDP packets on the AppleTalk network and placed them on the Ethernet network as IP packets.

Although a few sites used the actual SEAGATE multibus hardware, it served as a proof-of-concept and was eclipsed by the Kinetics FastPath and similar hardware gateways by other companies. However, many university and research Fastpath owners continued to run the Stanford gateway software (called KIP) inside the Kinetics box. This is because KIP was open source and local modifications and adaptations could be made.

By 1987, Apple had begun shipping Macintosh computers that were capable of having Ethernet connections directly, but the LocalTalk networking products prospered into the early 1990s, due to the popularity of Apple's plug-and-play networking.

Intel 8089

The Intel 8089 input/output coprocessor was available for use with the 8086/8088 central processor. It used the same programming technique as 8087 for input/output operations, such as transfer of data from memory to a peripheral device, and so reducing the load on the CPU.

Because IBM didn't use it in IBM PC design, it did not become well known; later I/O-coprocessors did not keep the x89 designation the way math coprocessors kept the x87 designation. It was used in the Apricot PC and the Intel Multibus iSBC-215 Hard disk drive controller. It was also used in the Altos 586 multi-user computer. Intel themselves used the 8089 in their reference designs (which they also commercialized) as System 86.


Multichannel may refer to:

Multichannel audio, i.e.

Stereophonic sound, namely two channel audio

Surround sound, more than two channel audio

Ambisonics, a studio or live way of recording with many channels

Offering multiple audio tracks on a broadcast channel: see Sound multiplex in broadcasting

Multichannel television sound, an American standard for analogue television

Having or offering multiple television channels: see Multichannel television

Multichannel Multipoint Distribution Service (MMDS), a standard for analogue television

Multichannel television in Canada

Multichannel television in the United States

Multichannel marketing

Multi-channel network, a YouTube classification of for-profit channels

Multichannel News

MPEG Multichannel

MADI, Multichannel Audio Digital Interface

McASP, Multichannel Audio Serial Port

Scanning Multichannel Microwave Radiometer

Joint multichannel trunking and switching system

Multibus, Multichannel I/O Bus

MVDDS, Multichannel Video and Data Distribution Service

MMDF, Multichannel Memorandum Distribution Facility

Omron Adept

Omron Adept Technology, Inc. is a multinational corporation with headquarters in Pleasanton, California (San Francisco Bay Area). The company focuses on industrial automation and robotics, including software and vision guidance. Adept has offices throughout the United States as well as in Dortmund, Germany, Paris, France, and Singapore. Adept was acquired by Omron in October 2015.


RMCDE (SuRveillance Message Conversion and Distribution Equipment) is the name of a system designed to distribute the surveillance information to a community of user systems.

A user of surveillance data in a general sense is defined in this context as any Air Traffic Control (ATC) subsystem having a requirement to receive at defined instants the best and most up-to-date position information for all air traffic of interest to this user (e.g. Operator Display System, Flight Data Processing System, ATC Tools, Flow-Control Management Units, Remote Terminal Maneuvering Area's, Military Units, etc.). The data can be originating from a surveillance sensor (e.g. radar, ADS-B receiver, Multi-lateration system) or a surveillance data processing system (e.g. ARTAS)

RMCDE is a Multibus II based multiprocessor system composed of a number of subsystems (processor and IO boards) connected through a parallel data bus.

In addition to its distribution function, the RMCDE offers additional capabilities to manage the surveillance data flow like data validation, conversion and filtering.

RMX (operating system)

iRMX is a real-time operating system designed specifically for use with the Intel 8080 and Intel 8086 family of processors. It is an acronym for Real-time Multitasking eXecutive. Intel developed iRMX in the 1970s and originally released RMX/80 in 1976 and RMX/86 in 1980 to support and create demand for their processors and Multibus system platforms.The functional specification for RMX/86 was authored by Bruce Schafer and Miles Lewitt and was completed in the summer of 1978 soon after Intel relocated the entire Multibus business from Santa Clara, California to Aloha, Oregon. Schafer and Lewitt went on each manage one of the two teams that developed the RMX/86 product for release on schedule in 1980.

Effective 2000 iRMX is supported, maintained, and licensed worldwide by TenAsys Corporation, under an exclusive licensing arrangement with Intel.

iRMX is a layered design: containing a kernel, nucleus, basic i/o system, extended i/o system and human interface. An installation need include only the components required: intertask synchronization, communication subsystems, a filesystem, extended memory management, command shell, etc. The native filesystem is specific to iRMX, but has many similarities to the original Unix (V6) filesystem, such as 14 character path name components, file nodes, sector lists, application readable directories, etc.

iRMX supports multiple processes (known as jobs in RMX parlance) and multiple threads are supported within each process (task). In addition, interrupt handlers and threads exist to run in response to hardware interrupts. Thus, iRMX is a multi-processing, multi-threaded, pre-emptive, real-time operating system (RTOS).


The STEbus (also called the IEEE-1000 bus) is a non-proprietary, processor-independent, computer bus with 8 data lines and 20 address lines. It was popular for industrial control systems in the late 1980s and early 1990s before the ubiquitous IBM PC dominated this market.

It remains a well-designed standard. Although no longer competitive in its original market, it is valid choice for hobbyists wishing to make 'home brew' computer systems. The Z80 and probably the CMOS 65C02 would be good processors to use. The standardized bus would allow hobbyists to interface to each other's designs.

SUN workstation

The SUN workstation was a modular computer system designed at Stanford University in the early 1980s. It became the seed technology for many commercial products, including the original workstations from Sun Microsystems.


Sun-1 was the first generation of UNIX computer workstations and servers produced by Sun Microsystems, launched in May 1982. These were based on a CPU board designed by Andy Bechtolsheim while he was a graduate student at Stanford University and funded by DARPA. The Sun-1 systems ran SunOS 0.9, a port of UniSoft's UniPlus V7 port of Seventh Edition UNIX to the Motorola 68000 microprocessor, with no window system. Early Sun-1 workstations and servers used the original Sun logo, a series of red "U"s laid out in a square, rather than the more familiar purple diamond shape used later.

The first Sun-1 workstation was sold to Solo Systems in May 1982. The Sun-1/100 was used in the original Lucasfilm EditDroid non-linear editing system.


The Sun-2 series of UNIX workstations and servers was launched by Sun Microsystems in November 1983. As the name suggests, the Sun-2 represented the second generation of Sun systems, superseding the original Sun-1 series. The Sun-2 series used a 10 MHz Motorola 68010 microprocessor with a proprietary Sun-2 Memory Management Unit (MMU), which enabled it to be the first Sun architecture to run a full virtual memory UNIX implementation, SunOS 1.0, based on 4.1BSD. Early Sun-2 models were based on the Intel Multibus architecture, with later models using VMEbus, which continued to be used in the successor Sun-3 and Sun-4 families.

Sun-2 systems were supported in SunOS until version 4.0.3.

A port to support Multibus Sun-2 systems in NetBSD was begun in January 2001 from the Sun-3 support in the NetBSD 1.5 release. Code supporting the Sun-2 began to be merged into the NetBSD tree in April 2001. sun2 is considered a tier 2 support platform as of NetBSD 7.0.1.


TenAsys (rhymes with tenacious) is a privately owned company providing real-time software and services based on the x86 Intel Architecture and Microsoft Windows operating system.


Xylogics or Xylogic Systems was started in 1970 by three former NASA employees. The company was originally named Xynetic Systems, but this name was already in use by a California company, so the group in Needham, MA changed their name in late 1970 to Xylogic Systems. Their original business was the design and development of computerized newspaper typesetting and editing systems. The first system was developed for the Daytona Beach News Journal, with the Farmington, NM newspaper getting the second system. By 1972, Xylogics had grown to more than 15 people, and moved to Natick, MA. The company used the GRI mini-computer, and custom designed many circuit boards to support disk drives, paper tape punches and readers, and automatic capture of newswire service feeds. By 1974, the company had developed a CRT editing station, and offered systems of up to 4 computers and more than 50 terminals for newspaper or in-plant publishing to perform editing and typesetting. About this time, a second division was created to design and build disk controllers for DEC computers, derived in part from the successful designs and manufacturing capability developed for the newspaper business. In 1976, a major customer of Xylogics, Dymo Graphics Systems, purchased the newspaper product line and hired most of the original developers. Dymo Graphics, of Wilmington, MA was the first company to develop laser technology for typesetting applications. Dymo Graphic Systems combined their typesetting equipment business with the Xylogics editing systems, and by 1978 had over 100 turnkey typesetting systems in use worldwide. The Xylogic Systems typesetting capability was the first with WYSIWYG (What You See Is What You Get) printing capability for Tabloid size page layout, and later full page layout. Capability included on-line classified ad capture with automated pricing, in addition to full page markup and typesetting. In 1977, Dymo was purchased by Eselte Corporation, who wanted control of the highly successful "Dymo Label Maker" consumer product.Eselte sold the newspaper and typesetting business to ITEK corporation in 1978, who wanted the laser technology IP (Intellectual Property). ITEK declined support to the newspaper and typesetting business, and in 1979, the newspaper product development and manufacturing staff of 150 engineers, technicians, assemblers, and field support personnel had dwindled to 2 by January, 1980.

Xylogics continued building disk and other controllers for DEC hardware.

They also built serial terminal servers from 4-port to 72-port units under the product name Annex.Xylogics was acquired by Bay Networks in December 1995 which in turn was acquired by Nortel in June 1998.

After Nortel's bankruptcy in 2009, support for the remaining Annex products ended up with Avaya. Xylogics was located in Burlington, MA.

The Multibus based Xylogics 450 SMD and Xylogics 451 ESMD disk controllers along with Interphase Multibus SMD disk controllers were significant to the workstation and minicomputer industry during the 1980s as a low cost interface the low cost, high performance, high capacity SMD and ESMD disk drives available at the time. Sun 1, Sun 2 and Sun 3 servers and Silicon Graphics IRIS, HP/Apollo all used Xylogics 450 and 451 disk controllers.

ISO standards by standard number

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