Futurebus

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Futurebus, or IEEE 896, 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, implementation of a chip-set based on the standard lacked industry leadership. It has seen little real-world use, although custom implementations continue to be designed and used throughout industry.

In computer architecture, 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. There are several local buses built into various types of computers to increase the speed of data transfer. Local buses for expanded memory and video boards are the most common.

Central processing unit Central component of any computer system which executes input/output, arithmetical, and logical operations

A central processing unit (CPU), also called a central processor or main processor, is the electronic circuitry within a computer that carries out the instructions of a computer program by performing the basic arithmetic, logic, controlling, and input/output (I/O) operations specified by the instructions. The computer industry has used the term "central processing unit" at least since the early 1960s. Traditionally, the term "CPU" refers to a processor, more specifically to its processing unit and control unit (CU), distinguishing these core elements of a computer from external components such as main memory and I/O circuitry.

Local area network computer network that connects devices over a small area

A local area network (LAN) is a computer network that interconnects computers within a limited area such as a residence, school, laboratory, university campus or office building. By contrast, a wide area network (WAN) not only covers a larger geographic distance, but also generally involves leased telecommunication circuits.

Contents

History

In the late 1970s, VMEbus 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.

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, which Eurocard does not define. It was first developed in 1981 and continues to see widespread use today.

Random-access memory Form of computer data storage

Random-access memory is a form of computer memory that can be read and changed in any order, typically used to store working data and machine code. A random-access memory device allows data items to be read or written in almost the same amount of time irrespective of the physical location of data inside the memory. In contrast, with other direct-access data storage media such as hard disks, CD-RWs, DVD-RWs and the older magnetic tapes and drum memory, the time required to read and write data items varies significantly depending on their physical locations on the recording medium, due to mechanical limitations such as media rotation speeds and arm movement.

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 wished. 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 to gain access to the bus at 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.

Asynchronous serial communication is a form of serial communication in which the communicating endpoints' interfaces are not continuously synchronized by a common clock signal. Instead of a common synchronization signal, the data stream contains synchronization information in form of start and stop signals, before and after each unit of transmission, respectively. The start signal prepares the receiver for arrival of data and the stop signal resets its state to enable triggering of a new sequence.

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 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. American Logic Machines (ALM) continues to build end to end system Futurebus hybrid solutions, including VME-to-Futurebus+ and other Bus-to-Futurebus bridge technologies.

Tektronix American test and measurement devices company

Tektronix, Inc., historically widely known as Tek, is an American company best known for manufacturing test and measurement devices such as oscilloscopes, logic analyzers, and video and mobile test protocol equipment.

American Logic Machines is a privately held embedded computing solutions provider based in San Jose, California in the United States. It is focused on the design, development and support of integrated computer solutions. It provides the electronic fabric for smart product design. ALM serves a variety of electronic industries worldwide: including automotive, aerospace, bio-medical, industrial, instrumentation, networking and consumer electronics. American Logic Machines has successfully delivered scalable solutions in the above-mentioned industries. ALM is a pioneer in the concept of Modularized Integration. Modular design and integration, is used extensively in building and deploying Data-Centers, Cloud-computing and in IoT.

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 submarines, 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+. It took another four years for the Futurebus+ Standard to be released by this time custom variation of Futurebus took the lead in industry.

Sonar technique that uses sound propagation

Sonar is a technique that uses sound propagation to navigate, communicate with or detect objects on or under the surface of the water, such as other vessels. Two types of technology share the name "sonar": passive sonar is essentially listening for the sound made by vessels; active sonar is emitting pulses of sounds and listening for echoes. Sonar may be used as a means of acoustic location and of measurement of the echo characteristics of "targets" in the water. Acoustic location in air was used before the introduction of radar. Sonar may also be used for robot navigation, and SODAR is used for atmospheric investigations. The term sonar is also used for the equipment used to generate and receive the sound. The acoustic frequencies used in sonar systems vary from very low (infrasonic) to extremely high (ultrasonic). The study of underwater sound is known as underwater acoustics or hydroacoustics.

<i>Seawolf</i>-class submarine class of US nuclear attack submarines

The Seawolf class is a class of nuclear-powered fast attack submarines (SSN) in service with the United States Navy. The class was the intended successor to the Los Angeles class, and design work began in 1983. A fleet of 29 submarines was to be built over a ten-year period, but that was reduced to 12 submarines. The end of the Cold War and budget constraints led to the cancellation of any further additions to the fleet in 1995, leaving the Seawolf class limited to just three boats. This, in turn, led to the design of the smaller Virginia class. The Seawolf class cost about $3 billion per unit, making it the most expensive SSN submarine and second most expensive submarine ever, after the French SSBN Triomphant class.

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. Custom implementations of the Futurebus technology are currently used as backplane technologies for high-end network applications, enterprise class routers, high performance blade servers, and application with high demand-content such as video on demand.

Futurebus effort did act as a catalyst for simpler serial technologies. A group then organized to create a system aimed directly at this need, which eventually led to Scalable Coherent Interface (SCI). 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 ahead of its time in the 1980s. VME and other parallel bus standards are still trying to adapt concepts that are implemented in the Futurebus, specially in high performance applications.

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. Futurebus+ custom chips support advanced Symmetric and Asymmetric versions of Unix-Like operating systems supported by companies such as American Logic Machines.

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 experiments in the 1980s and 1990s.

Description

Futurebus is described in just a few IEEE standards:

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.

See also

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Eurocard (printed circuit board)

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Expansion card a printed circuit board that can be inserted into an electrical connector, or expansion slot on a computer motherboard, backplane or riser card to add functionality to a computer system via the expansion bus

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NuBus

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S-100 bus

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Scalable Coherent Interface organization

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