This is very important where virtual memory resources that are not contiguous are allocated by an OS in physical memory. By maintaining the VME side of the application, the combination system is afforded all of the proven advantages of the bus that has supported industrial applications for well over a decade. The firmly entrenched hundreds of vendors offering supporting products are testimony to the success of the bus. The cards tend to stay on the market far longer than components in the PC realm, which is driven by the transient desires of desktop users. Devices in the medical imaging hardware backplane, regardless of their bus architecture, can be directly controlled from a remote workstation.
Latencies are low enough that accessing the remote bus has the appearance of a local transaction.
For example, the operator of a large piece of equipment that is in the room with a patient can control its backplane from a remote console and a Sun, SGI, or other workstation. All seven VME interrupts can be monitored and acknowledged from the PCI host system. Consequently, the host system can be notified asynchronously whenever a VME-bus card requires servicing, without the need for polling. The VME can interrupt the PCI bus, and the PCI bus can send an interrupt to the VME bus. Such a procedure would require using many ISO layers in a system utilizing Ethernet with a single-board computer.