Before the coming of CompactPCI technology, VME reigned supreme in the worlds of high-end telecom, military, industrial, and other real-time computing systems. VME has a huge installed base. VME uses a completely memory mapped scheme, and every device can be viewed as an address, or block of addresses. Addresses and data are not multiplexed - it’s an asynchronous bus, so data can be transferred to each board at its own optimum speed. A typical transfer consists of an arbitration cycle (to gain bus control), an address cycle (to select the reg ister) and the actual data cycle. Read, write, modify and block transfers are supported.