An open computer bus standard, defined originally by Motorola, Mostek and Signetics. VMEbus is used primarily for industrial applications.

The specifications of VMEbus (IEEE-1014-1987, VME64 and VME64x being the most widespread variants) call for standardization on connectors, sizes of modules, interconnection on the backplane, and numerous electrical and protocol issues. The oldest standard is for an asynchronous system which allows up to 40Mbyte/s of data transfer between the various components, which includes up to 32 bits of address bus, 32 bits of data bus, and a variety of control lines providing interrupt and multiprocessing capabilities.

VMEbus was important in its time as it predated more widespread standard busses while providing features found (at the time) only in proprietary vendor-specific busses. Additionally, VMEbus provided control features not available on the competing open busses at the time such as ISA, found in many personal computers.

Many pieces of VMEbus equipment, utilizing the 1987 spec, are still in operation today. The telecommunications and aerospace industries built many products around the VMEbus -- in fact, the 1998 Mars Pathfinder used VMEbus to communicate between the components in the spacecraft. Many commercial jetliners have VMEbus components, and Motorola used VMEbus in much of their modem and CSU/DSU concentration hardware.

Later extensions of the VMEbus standards (VME64 and VME64x) allowed for higher bandwidth and specified more sturdy mechanical connectors, as well as providing more power for high-current applications. VME64x supports up to 160 Mbyte/s of data transfer between the components on a bus with 160 connectors. It allows for "hot swap" and "hot plug" exchange of components and still maintains backwards-compatibility with earlier VMEbus equipment.

The latest standard, VME320, was drafted by Arizona Digital, Inc., who owns patents on the backplane technology. They allow any company to freely manufacture modules utilizing the standard, however. VME320 fixes earlier timing issues with the asynchronous data flow to allow up to 320 Mbyte/s across the bus (with peaks over 500 Mbyte/s).

VMEbus is supported in more than 100 operating systems, including commercial/industrial variants of Solaris, Linux, DOS, Windows, and QNX.

For more information, see the VMEbus Usenet newsgroup, comp.arch.bus.vmebus or the VMEbus FAQ, at http://www.vita.com/vmefaq/index.html.