The VME bus address space of the memory card is mapped into process address space. Firmware on the card handles communication across the network, so as to keep the memory contents of all connected cards consistent. Reflective shared memory is slower than real main memory but faster than socket I/O. Its performance is essentially that of programmed I/O to the VME bus, which is discussed under "PIO Access".
Reflective shared memory systems are available for Silicon Graphics equipment from several third-party vendors. The details of the software interface differ with each vendor. However, in most cases you use mmap() to map the shared segment into your process's address space (see Chapter 4, "Managing Virtual Memory in a RealTime Program" as well as the usrvme(7) reference page).