Home / Computer / So What Is The VME Bus?


VME stands for Versa Module Europa. It’s a computer bus that was first created in 1981 for Motorola 68000 CPUs and then taken up for so many applications that the IEC standardised it and ANSI/IEEE followed suit with 1014-1987. It grew out of Eurocard standards but Eurocard does not define a signalling system and the VME bus developed its own.

The standard as originally developed was a 16-bit bus of a size to go into the DIN connectors of the Eurocard at that time. There have been a number of updates since then facilitating wider bus widths and the VME64 has a 64-bit bus and a 32-bit bus. Typically, VME64 performs at 40 MB/s. There is a hot-swap plug and play version (VME64x) and linkage standards that allow interconnection of VME systems. Synchronous protocols have also been developed.

VMEbusExtensions have enabled “sideband” communication channels to run parallel to VME and these are largely available under proprietary brand names. StarFabric, InfiniBand and RapidIO are examples.

Developments growing out of the VMEbus have included VXIbus and STEbus. There are those who say – and, in fact, have been saying for a number of years – that the VMEbus has had its day as a leading OEM bus. Each time we hear that, it seems that someone develops a new application for which VMEbus is just right. Now, with the Intel Core 2 Duo processor coming on the scene, VME has a new lease of life. Its functionality for new applications has proved difficult for competing systems to outperform and it is still very reliable in cost and performance.

In addition, the large number of existing VME implementations (including, but not restricted to, military and industrial systems) need an upgrade path that won’t break the bank and the developing VME bus offers that. Take the flexible I/O of VME and add the performance of the new Intel processors and the question is not when will VME die but what on earth can take its place?