Multibus
Encyclopedia
Multibus is a computer bus
standard used in industrial systems. It was developed by Intel Corporation
and was adopted as the IEEE 796 bus.
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. Being a well-defined and well-documented industry standard allowed a Multibus-compatible industry to grow around it. There were 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. This allowed complex systems to be built from commercial off-the-shelf
hardware. It 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 is 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 controller
s, Ciprico Tapemaster 1/2 inch tape controllers, Sky Floating Point Processor and Systech 16 port Terminal Interfaces to configure the system as a workstation
or a file server
. Other workstation vendors who used Multibus-based designs included HP
/Apollo
and Silicon Graphics
IRIS
.
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.
The standard Multibus form factor was a 12 inches (304.8 mm), 6.75 inches (171.5 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.
Central Line
signals control system was supplied by Westinghouse now Invensys
and commissioned in the late 1990s. The Central Line is an automatic train operation line. Automatic train protection is by trackside and train borne equipment that does not use Multibus. It is the automatic train supervision elements that use a mix of iRMX on Multibus, and Sun Solaris operating system
on Sparc
computers. 16 Multibus local site computers are distributed along the Central Line together with 6 central Multibus computers at the control centre. All 22 Multibus computers are dual redundant. CLSCS Multibus continues in full operation in 2011.
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.
Computer bus
In computer architecture, a bus is a subsystem that transfers data between components inside a computer, or between computers.Early computer buses were literally parallel electrical wires with multiple connections, but the term is now used for any physical arrangement that provides the same...
standard used in industrial systems. It was developed by Intel Corporation
Intel Corporation
Intel Corporation is an American multinational semiconductor chip maker corporation headquartered in Santa Clara, California, United States and the world's largest semiconductor chip maker, based on revenue. It is the inventor of the x86 series of microprocessors, the processors found in most...
and was adopted as the IEEE 796 bus.
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. Being a well-defined and well-documented industry standard allowed a Multibus-compatible industry to grow around it. There were 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. This allowed complex systems to be built from commercial off-the-shelf
Commercial off-the-shelf
In the United States, Commercially available Off-The-Shelf is a Federal Acquisition Regulation term defining a nondevelopmental item of supply that is both commercial and sold in substantial quantities in the commercial marketplace, and that can be procured or utilized under government contract...
hardware. It 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 is Sun Microsystems
Sun Microsystems
Sun Microsystems, Inc. was a company that sold :computers, computer components, :computer software, and :information technology services. Sun was founded on February 24, 1982...
with their Sun 1 and Sun 2 workstations. Sun built custom designed CPU, memory, SCSI
SCSI
Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it...
, and video display boards and then added 3com
3Com
3Com was a pioneering digital electronics manufacturer best known for its computer network infrastructure products. The company was co-founded in 1979 by Robert Metcalfe, Howard Charney, Bruce Borden, and Greg Shaw...
Ethernet
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
networking boards, Xylogics
Xylogics
Xylogics started out building disk and other controllers for DEC hardware.They also built serial terminal servers from 4-port to 72-port units.Xylogics was acquired by Bay Networks in December 1995 which in turn was acquired by Nortel in June 1998....
SMD disk controller
Disk controller
The disk controller is the circuit which enables the CPU to communicate with a hard disk, floppy disk or other kind of disk drive.Early disk controllers were identified by their storage methods and data encoding. They were typically implemented on a separate controller card...
s, Ciprico Tapemaster 1/2 inch tape controllers, Sky Floating Point Processor and Systech 16 port Terminal Interfaces to configure the system as a workstation
Workstation
A workstation is a high-end microcomputer designed for technical or scientific applications. Intended primarily to be used by one person at a time, they are commonly connected to a local area network and run multi-user operating systems...
or a file server
File server
In computing, a file server is a computer attached to a network that has the primary purpose of providing a location for shared disk access, i.e. shared storage of computer files that can be accessed by the workstations that are attached to the computer network...
. Other workstation vendors who used Multibus-based designs included HP
Hewlett-Packard
Hewlett-Packard Company or HP is an American multinational information technology corporation headquartered in Palo Alto, California, USA that provides products, technologies, softwares, solutions and services to consumers, small- and medium-sized businesses and large enterprises, including...
/Apollo
Apollo Computer
Apollo Computer, Inc., founded 1980 in Chelmsford, Massachusetts by William Poduska and others, developed and produced Apollo/Domain workstations in the 1980s. Along with Symbolics and Sun Microsystems, Apollo was one of the first vendors of graphical workstations in the 1980s...
and Silicon Graphics
Silicon Graphics
Silicon Graphics, Inc. was a manufacturer of high-performance computing solutions, including computer hardware and software, founded in 1981 by Jim Clark...
IRIS
Iris
Iris commonly refers to:* Iris , part of the eye* Iris * Iris , a feminine given name* Iris , a Greek goddess* Iris , a genus of flowering plantsIris may also refer to:-Places:...
.
Multibus architecture
Multibus is an asynchronousAsynchronous I/O
Asynchronous I/O, or non-blocking I/O, is a form of input/output processing that permits other processing to continue before the transmission has finished....
bus that accommodates devices with various transfer rates while maintaining maximum throughput
Throughput
In communication networks, such as Ethernet or packet radio, throughput or network throughput is the average rate of successful message delivery over a communication channel. This data may be delivered over a physical or logical link, or pass through a certain network node...
. It had 20 address lines so it could address up to 1 Mb
Megabit
The megabit is a multiple of the unit bit for digital information or computer storage. The prefix mega is defined in the International System of Units as a multiplier of 106 , and therefore...
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
Multi-master bus
A multi-master bus is a computer bus in which there are multiple bus master nodes present on the bus.This is used when multiple nodes on the bus must/need to initiate transfer....
functionality that allowed it to share the Multibus with multiple processors and other DMA
DMA
DMA can refer to:* DMA , a defunct dance music magazine* Dallas Museum of Art, an art museum in Texas, USA* Danish Music Awards, an award show held in Denmark since 1989...
devices.
The standard Multibus form factor was a 12 inches (304.8 mm), 6.75 inches (171.5 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 (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. 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/10MHz bus, at 40Mbyte/s. Card sizes are 3U x 220mm, and 6U x 220mm. These cards are larger than the VME Eurocard sizes which are 3U/6U x 160mm. Uses TTL ('Fast' series) gates for drivers and the Backplane Connectors are DIN41612 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 Intel iRMX operating system is used in the majority core systems on CLSCS the London UndergroundLondon Underground
The London Underground is a rapid transit system serving a large part of Greater London and some parts of Buckinghamshire, Hertfordshire and Essex in England...
Central Line
Central Line
The Central line is a London Underground line, coloured red on the tube map. It is a deep-level "tube" line, running east-west across London, and, at , has the greatest total length of track of any line on the Underground. Of the 49 stations served, 20 are below ground...
signals control system was supplied by Westinghouse now Invensys
Invensys
Invensys plc is a global engineering and information technology company headquartered in London, United Kingdom. It was formed in 1999 through the merger of BTR plc and Siebe plc. It has offices in more than 50 countries and its products are sold in around 180 countries.Invensys is organised into...
and commissioned in the late 1990s. The Central Line is an automatic train operation line. Automatic train protection is by trackside and train borne equipment that does not use Multibus. It is the automatic train supervision elements that use a mix of iRMX on Multibus, and Sun Solaris operating system
Solaris Operating System
Solaris is a Unix operating system originally developed by Sun Microsystems. It superseded their earlier SunOS in 1993. Oracle Solaris, as it is now known, has been owned by Oracle Corporation since Oracle's acquisition of Sun in January 2010....
on Sparc
SPARC
SPARC is a RISC instruction set architecture developed by Sun Microsystems and introduced in mid-1987....
computers. 16 Multibus local site computers are distributed along the Central Line together with 6 central Multibus computers at the control centre. All 22 Multibus computers are dual redundant. CLSCS Multibus continues in full operation in 2011.
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.