Multibus

Multibus is a computer bus standard used in industrial systems. It was developed by Intel Corporation and was adopted as the IEEE 796 bus. 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. 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. 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. Other workstation vendors who used Multibus-based designs included HP/Apollo and Silicon Graphics. 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. 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.