Futurebus
Encyclopedia
Futurebus is a computer bus
standard, intended to replace all local bus
connections in a computer, including the CPU
, memory
, plug-in cards and even, to some extent, LAN
links between machines. The effort started in 1979 and didn't complete until 1987, and then immediately went into a redesign that lasted until 1994. By this point everyone involved lost interest, and Futurebus saw little use.
was faster than the parts plugged into it. It was quite reasonable to connect a CPU
and RAM to VME on separate cards to build a computer. However, as the speed of the CPUs and RAM rapidly increased, VME was quickly overwhelmed. Increasing the speed of VME was not easy, because all of the parts plugged into it would have to be able to support these faster speeds as well.
Futurebus looked to fix these problems and create a successor to systems like VMEbus with a system that could grow in speed without affecting existing devices. In order to do this the primary technology of Futurebus was built using asynchronous links, allowing the devices plugged into it to talk at whatever speed they could. Another problem that needed to be addressed was the ability to have several cards in the system as "masters", allowing Futurebus to build multiprocessor machines. This required some form of "distributed arbitration" to allow the various cards gain access to the bus from any point, as opposed to VME which put a single master in slot 0 with overall control. In order to have a clear performance benefit, Futurebus was designed to have the performance needed ten years in the future.
Typical IEEE standards start with a company building a device, and then submitting it to the IEEE for the standardization effort. In the case of Futurebus this was reversed, the whole system was being designed as during the standardization effort. This proved to be its downfall. As companies came to see Futurebus as the system, they all joined in. Soon the standards meetings had hundreds of people attending, all of them demanding that their particular needs and wants be included. As the complexity grew, the standards process slowed. In the end it took eight long years before the specification was finally agreed on in 1987. Tektronix
did make a few workstations based on Futurebus.
That was just in time for the US Navy who had been looking for a new high-speed system for the Next Generation Computer Resources (NGCR) project for passing sonar
data around in their newly designed Seawolf class submarine
s, and they said they would standardize on Futurebus if only a few more changes would be made. Seeing a potential massive government buy, the additions effort started immediately on Futurebus+. This also had the unexpected side effect of killing any effort to produce Futurebus system while everyone waited for the new version to come out, "real soon now". Real soon turned out to be another four years, and when the resulting Futurebus+ was released, no one was interested any longer.
All of the Futurebus+ proponents had their idea of what Futurebus+ should be. This degenerated into "profiles", different versions of Futurebus+ targeted towards a particular market. Boards that were compliant with one Futurebus+ profile were not guaranteed to work with boards built to a different profile. The Futurebus+ standards development politics got so complicated that the IEEE 896 committee split from the IEEE Microcomputer Standards Committee and formed the IEEE Bus Architecture Standards Committee (BASC).
In the end very little use of Futurebus was attempted. The decade-long performance gap they gave the system had evaporated in the decade-long standards process, and conventional local bus systems like PCI
were close in performance terms. Meanwhile the VME ecosystem had evolved to such a degree that it continues to be used today, another decade on. The Futurebus technology is currently used as an internal backplane technology for systems such as routers.
However the Futurebus effort did act as a catalyst for change in other ways. After the 1987 version shipped and the Futurebus+ effort started, a number of the original designers realized the effort was doomed. One member did a quick back-of-the-envelope calculation and showed that by the time Futurebus+ shipped, it would already be too slow for the supercomputer
market. A group then organized to create a system aimed directly at this need, which eventually led to Scalable Coherent Interconnect
. Meanwhile another member decided to simple re-create the entire concept on a much simpler basis, which resulted in QuickRing
. Due to the simplicity of these standards, both standards were completed before Futurebus+.
Futurebus was the source of some of the original work on Cache Coherency
, Live Insertion of boards, and Trapezoidal Transceivers. Trapezoidal Transceivers have a controlled risetime and make backplane and bus design much simpler. The original Trapezoidal Transceivers were made by National Semiconductor
. Newer Futurebus+ transceivers that meet the IEEE Std 1194.1-1991 Backplane Transceiver Logic (BTL) standard are still made by Texas Instruments
. Futurebus+ was used as the I/O bus in the DEC 4000 AXP
and DEC 10000 AXP
systems. Futurebus+ FDDI boards are still supported in the OpenVMS
operating system.
Many of the technical features (asynchronous data bus, distributed bus arbitration, large board size) are shared with IEEE standard FASTBUS
.
FASTBUS was used as a data acquisition system in many high-energy physics in the 1980s and 1990s.
Futurebus systems were implemented with 9Ux280 Eurocard mechanics using 96-pin DIN
connectors resulting in a backplane that supported both 16 and 32 bit bus widths.
To understand Futurebus+ you need to read many IEEE standards;
896.2 contains three Profiles for target markets, A for general purpose systems, B for an I/O bus, and F for a Futurebus+ will all the options that will make it go fast. Profile A was sponsored by the VMEbus
community. Profile B was sponsored by Digital Equipment Corporation
and implemented in VAX
and Alpha
systems as an I/O bus. Profile F was sponsored by John Theus while he worked at Tektronix
and was intended for high end workstations.
Futurebus+ supports bus widths from 32 to 256 bits. It is possible to build a board that supports all of these bus widths and will interoperate with boards that only support a subset. Split bus transactions are supported so that slow response to a read or write will not tie up the backplane bus. Cache Coherence, implemented using the MESI protocols, was very complicated but significantly improved performance. Futurebus+ was one of the first open standards to support Live Insertion which allowed boards to be replaced while the system was running.
Futurebus+ boards are 12SUx12SU Hard Metric size defined in the IEEE 1301 standards.
One of the most elegant features of the Futurebus design is its distributed bus arbitration mechanism. See US patent number 5060139 for more information. In the end this was replaced by a central arbiter.
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, intended to replace all local bus
Local bus
In computer science, a local bus is a computer bus that connects directly, or almost directly, from the CPU to one or more slots on the expansion bus. The significance of direct connection to the CPU is avoiding the bottleneck created by the expansion bus, thus providing fast throughput...
connections in a computer, including the CPU
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
, memory
Computer storage
Computer data storage, often called storage or memory, refers to computer components and recording media that retain digital data. Data storage is one of the core functions and fundamental components of computers....
, plug-in cards and even, to some extent, LAN
Local area network
A local area network is a computer network that interconnects computers in a limited area such as a home, school, computer laboratory, or office building...
links between machines. The effort started in 1979 and didn't complete until 1987, and then immediately went into a redesign that lasted until 1994. By this point everyone involved lost interest, and Futurebus saw little use.
History
The original in the late 1970s, VMEbusVMEbus
VMEbus is a computer bus standard, originally developed for the Motorola 68000 line of CPUs, but later widely used for many applications and standardized by the IEC as ANSI/IEEE 1014-1987. It is physically based on Eurocard sizes, mechanicals and connectors , but uses its own signalling system,...
was faster than the parts plugged into it. It was quite reasonable to connect a CPU
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
and RAM to VME on separate cards to build a computer. However, as the speed of the CPUs and RAM rapidly increased, VME was quickly overwhelmed. Increasing the speed of VME was not easy, because all of the parts plugged into it would have to be able to support these faster speeds as well.
Futurebus looked to fix these problems and create a successor to systems like VMEbus with a system that could grow in speed without affecting existing devices. In order to do this the primary technology of Futurebus was built using asynchronous links, allowing the devices plugged into it to talk at whatever speed they could. Another problem that needed to be addressed was the ability to have several cards in the system as "masters", allowing Futurebus to build multiprocessor machines. This required some form of "distributed arbitration" to allow the various cards gain access to the bus from any point, as opposed to VME which put a single master in slot 0 with overall control. In order to have a clear performance benefit, Futurebus was designed to have the performance needed ten years in the future.
Typical IEEE standards start with a company building a device, and then submitting it to the IEEE for the standardization effort. In the case of Futurebus this was reversed, the whole system was being designed as during the standardization effort. This proved to be its downfall. As companies came to see Futurebus as the system, they all joined in. Soon the standards meetings had hundreds of people attending, all of them demanding that their particular needs and wants be included. As the complexity grew, the standards process slowed. In the end it took eight long years before the specification was finally agreed on in 1987. Tektronix
Tektronix
Tektronix, Inc. is an American company best known for its test and measurement equipment such as oscilloscopes, logic analyzers, and video and mobile test protocol equipment. In November 2007, Tektronix became a subsidiary of Danaher Corporation....
did make a few workstations based on Futurebus.
That was just in time for the US Navy who had been looking for a new high-speed system for the Next Generation Computer Resources (NGCR) project for passing sonar
Sonar
Sonar is a technique that uses sound propagation to navigate, communicate with or detect other vessels...
data around in their newly designed Seawolf class submarine
Seawolf class submarine
The Seawolf class is a class of nuclear-powered fast attack submarines in service with the United States Navy. The class was the intended successor to the , ordered at the end of the Cold War in 1989. At one time, an intended fleet of 29 submarines was to be built over a ten-year period, later...
s, and they said they would standardize on Futurebus if only a few more changes would be made. Seeing a potential massive government buy, the additions effort started immediately on Futurebus+. This also had the unexpected side effect of killing any effort to produce Futurebus system while everyone waited for the new version to come out, "real soon now". Real soon turned out to be another four years, and when the resulting Futurebus+ was released, no one was interested any longer.
All of the Futurebus+ proponents had their idea of what Futurebus+ should be. This degenerated into "profiles", different versions of Futurebus+ targeted towards a particular market. Boards that were compliant with one Futurebus+ profile were not guaranteed to work with boards built to a different profile. The Futurebus+ standards development politics got so complicated that the IEEE 896 committee split from the IEEE Microcomputer Standards Committee and formed the IEEE Bus Architecture Standards Committee (BASC).
In the end very little use of Futurebus was attempted. The decade-long performance gap they gave the system had evaporated in the decade-long standards process, and conventional local bus systems like PCI
Peripheral Component Interconnect
Conventional PCI is a computer bus for attaching hardware devices in a computer...
were close in performance terms. Meanwhile the VME ecosystem had evolved to such a degree that it continues to be used today, another decade on. The Futurebus technology is currently used as an internal backplane technology for systems such as routers.
However the Futurebus effort did act as a catalyst for change in other ways. After the 1987 version shipped and the Futurebus+ effort started, a number of the original designers realized the effort was doomed. One member did a quick back-of-the-envelope calculation and showed that by the time Futurebus+ shipped, it would already be too slow for the supercomputer
Supercomputer
A supercomputer is a computer at the frontline of current processing capacity, particularly speed of calculation.Supercomputers are used for highly calculation-intensive tasks such as problems including quantum physics, weather forecasting, climate research, molecular modeling A supercomputer is a...
market. A group then organized to create a system aimed directly at this need, which eventually led to Scalable Coherent Interconnect
Scalable Coherent Interconnect
SCI, for Scalable Coherent Interface, is a high-speed interconnect standard for shared memory multiprocessing and message passing. The IEEE Std 1596-1992, IEEE Standard for Scalable Coherent Interface was approved by the IEEE standards board on March 19, 1992...
. Meanwhile another member decided to simple re-create the entire concept on a much simpler basis, which resulted in QuickRing
QuickRing
QuickRing was a gigabit-rate interconnect that combined the functions of a computer bus and a network. It was designed at Apple Computer as a multimedia system to run "on top" of existing local bus systems inside a computer, but was later taken over by National Semiconductor and repositioned as an...
. Due to the simplicity of these standards, both standards were completed before Futurebus+.
Futurebus was the source of some of the original work on Cache Coherency
Cache coherency
In computing, cache coherence refers to the consistency of data stored in local caches of a shared resource.When clients in a system maintain caches of a common memory resource, problems may arise with inconsistent data. This is particularly true of CPUs in a multiprocessing system...
, Live Insertion of boards, and Trapezoidal Transceivers. Trapezoidal Transceivers have a controlled risetime and make backplane and bus design much simpler. The original Trapezoidal Transceivers were made by National Semiconductor
National Semiconductor
National Semiconductor was an American semiconductor manufacturer, that specialized in analog devices and subsystems,formerly headquartered in Santa Clara, California, USA. The products of National Semiconductor included power management circuits, display drivers, audio and operational amplifiers,...
. Newer Futurebus+ transceivers that meet the IEEE Std 1194.1-1991 Backplane Transceiver Logic (BTL) standard are still made by Texas Instruments
Texas Instruments
Texas Instruments Inc. , widely known as TI, is an American company based in Dallas, Texas, United States, which develops and commercializes semiconductor and computer technology...
. Futurebus+ was used as the I/O bus in the DEC 4000 AXP
DEC 4000 AXP
The DEC 4000 AXP is a series of departmental server computers developed and manufactured by Digital Equipment Corporation introduced on 10 November 1992...
and DEC 10000 AXP
DEC 7000/10000 AXP
The DEC 7000 AXP and DEC 10000 AXP are a series of high-end multiprocessor server computers developed and manufactured by Digital Equipment Corporation, introduced on 10 November 1992...
systems. Futurebus+ FDDI boards are still supported in the OpenVMS
OpenVMS
OpenVMS , previously known as VAX-11/VMS, VAX/VMS or VMS, is a computer server operating system that runs on VAX, Alpha and Itanium-based families of computers. Contrary to what its name suggests, OpenVMS is not open source software; however, the source listings are available for purchase...
operating system.
Many of the technical features (asynchronous data bus, distributed bus arbitration, large board size) are shared with IEEE standard FASTBUS
FASTBUS
FASTBUS is a computer bus standard, originally intended to replace CAMAC in high-speed, large-scale data acquisition.- Description :...
.
FASTBUS was used as a data acquisition system in many high-energy physics in the 1980s and 1990s.
Description
Futurebus is described in just a few IEEE standards;- 896.1-1987 IEEE Standard Backplane Bus Specifications for Multiprocessor Architectures: Futurebus
- 1101-1987 IEEE Standard for Mechanical Core Specifications for Microcomputers Using IEC 603-2 Connectors
Futurebus systems were implemented with 9Ux280 Eurocard mechanics using 96-pin DIN
Din
DIN or Din or din can have several meanings:* A din is a loud noise.* Dīn, an Arabic term meaning "religion" or "way of life".* Din is one of the ten aspects of the Ein Sof in Kabbalah ....
connectors resulting in a backplane that supported both 16 and 32 bit bus widths.
To understand Futurebus+ you need to read many IEEE standards;
- 896.1-1991 IEEE Standard for Futurebus+ — Logical Protocol Specification
- 896.2-1991 IEEE Standard Backplane Bus Specification for Multiprocessor Architectures: Futurebus+
- 896.3-1993 IEEE recommended practice for Futurebus+
- 896.4-1993 IEEE Standard for Conformance Test Requirements for Futurebus+
- 896.5-1993 IEEE Standard for Futurebus+, Profile M (Military)
- 896.6 Futurebus+ telecommunications systems, profile T (telecommunications)
- 896.7 Interconnect between Futurebus+ systems
- 896.8 Small computer expandibility module for Futurebus+ systems, profile D (desktop)
- 896.9-1994 Fault tolerant extensions to the Futurebus+ architecture
- 896.10-1997 Standard for Futurebus+ Spaceborne Systems - Profile S
- 896.11 Standard for IEEE 1355 Links on Futurebus+ Backplane Connector
- 896.12 Standard for Fault Tolerance Classification of Computer-Based Systems
- 1194.1-1991 IEEE Standard for Electrical Characteristics of Backplane Transceiver Logic (BTL) Interface Circuits
- 1301 Standard for Metric Equipment Practice for Microcomputers - Coordination Document
- 1301.1-1991 IEEE Standard for a Metric Equipment Practice for Microcomputers—Convection-Cooled with 2 mm Connectors
- 1156.1 Standard Microprocessor Environmental Specifications for Computer Modules
- EIA IS-64 (1991) 2 mm Two-Part Connectors for Use with Printed Boards and Backplanes
896.2 contains three Profiles for target markets, A for general purpose systems, B for an I/O bus, and F for a Futurebus+ will all the options that will make it go fast. Profile A was sponsored by the VMEbus
VMEbus
VMEbus is a computer bus standard, originally developed for the Motorola 68000 line of CPUs, but later widely used for many applications and standardized by the IEC as ANSI/IEEE 1014-1987. It is physically based on Eurocard sizes, mechanicals and connectors , but uses its own signalling system,...
community. Profile B was sponsored by Digital Equipment Corporation
Digital Equipment Corporation
Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...
and implemented in VAX
VAX
VAX was an instruction set architecture developed by Digital Equipment Corporation in the mid-1970s. A 32-bit complex instruction set computer ISA, it was designed to extend or replace DEC's various Programmed Data Processor ISAs...
and Alpha
DEC Alpha
Alpha, originally known as Alpha AXP, is a 64-bit reduced instruction set computer instruction set architecture developed by Digital Equipment Corporation , designed to replace the 32-bit VAX complex instruction set computer ISA and its implementations. Alpha was implemented in microprocessors...
systems as an I/O bus. Profile F was sponsored by John Theus while he worked at Tektronix
Tektronix
Tektronix, Inc. is an American company best known for its test and measurement equipment such as oscilloscopes, logic analyzers, and video and mobile test protocol equipment. In November 2007, Tektronix became a subsidiary of Danaher Corporation....
and was intended for high end workstations.
Futurebus+ supports bus widths from 32 to 256 bits. It is possible to build a board that supports all of these bus widths and will interoperate with boards that only support a subset. Split bus transactions are supported so that slow response to a read or write will not tie up the backplane bus. Cache Coherence, implemented using the MESI protocols, was very complicated but significantly improved performance. Futurebus+ was one of the first open standards to support Live Insertion which allowed boards to be replaced while the system was running.
Futurebus+ boards are 12SUx12SU Hard Metric size defined in the IEEE 1301 standards.
One of the most elegant features of the Futurebus design is its distributed bus arbitration mechanism. See US patent number 5060139 for more information. In the end this was replaced by a central arbiter.
See also
- InfiniBandInfiniBandInfiniBand is a switched fabric communications link used in high-performance computing and enterprise data centers. Its features include high throughput, low latency, quality of service and failover, and it is designed to be scalable...
- QuickRingQuickRingQuickRing was a gigabit-rate interconnect that combined the functions of a computer bus and a network. It was designed at Apple Computer as a multimedia system to run "on top" of existing local bus systems inside a computer, but was later taken over by National Semiconductor and repositioned as an...
- SCIScalable Coherent InterconnectSCI, for Scalable Coherent Interface, is a high-speed interconnect standard for shared memory multiprocessing and message passing. The IEEE Std 1596-1992, IEEE Standard for Scalable Coherent Interface was approved by the IEEE standards board on March 19, 1992...
- Bus topology
- The Futurebus+ Handbook, John Theus, VITA
- Futurebus+ Handbook for Digital Systems, Digital Equipment CorporationDigital Equipment CorporationDigital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...
- FASTBUSFASTBUSFASTBUS is a computer bus standard, originally intended to replace CAMAC in high-speed, large-scale data acquisition.- Description :...