Futurebus

Futurebus (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 (IEEE 896) standards lacked industry leadership. Although custom implementations continue to be designed and used throughout industry.

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.

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 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) is a pioneer in scalable backplane technologies, working with partners like Texas Instruments(TI) and Bus connector manufacturers (Molex Inc, Tyco Electronic etc. ..) continues to build end to end system Futurebus hybrid solutions. ALM is a provider of custom chip-sets solutions for clients, including VME-to-PCIX, VME-to-Futurebus+ and other Bus-to-Futurebus bridge technologies.

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