The VME64 specification establishes a framework for 8-, 16-, 32, and 64-bit parallel-bus
computer architectures that can implement single and multiprocessor systems. It is based on
the VMEbus specification released by the VMEbus Manufacturers Group (now VITA) in August
of 1982. This bus includes the initial four basic subbuses: (1) data transfer bus, (2) priority
interrupt bus, (3) arbitration bus, and (4) utility bus. Other architectures with other subbuses
are possible within this VME framework.
The data transfer bus will support 8-, 16-, 32-, and 64-bit data transfers in multiplexed and non
multiplexed form. The transfer protocols are asynchronous with varying degrees of
handshaking dependent on the speeds required. The priority interrupt subsystem provides
real-time interrupt services to the system. The allocation of bus mastership is performed by
the arbitration subsystem which allows the implementation of several prioritization
algorithms. The utility bus provides the system with power plus power-up and power-down
synchronization. The mechanical specifications of boards, backplanes, subracks, and
enclosures are based on IEC 297 and IEEE 1101.1 specifications, also known as the Eurocard
form factor. Additional standards exist that can be used as sub-busses to this architecture for
data transfers transactions, peripheral interfaces and intra-crate communications among
compatible modules.