Key to system designs that provide high-availability is the option to hot swap devices, in other words, perform "live" insertion and removal of hardware without disrupting the host system or application. An example would be pulling out the CPU or I/O board and replacing it with another, with no downtime of either hardware or software anywhere in the system. Not only can you replace failed devices in a hot-swap system, but also online upgrades are possible. For example, you can upgrade an entire single-board computer within the system, or increase the memory on a particular board, simply by swapping out the cards.
When live insertion, or "hot swap," is mentioned, it is usually associated with CompactPCI solutions. The predominant association of hot swap and CompactPCI seems puzzling when you consider that a high percentage of the existing infrastructure is VME-based, and that VME now provides a cost effective migration path to live insertion technology upgrades. Part of the reason for the obscure association between VME and "Hot Swap" is that the CompactPCI Live Insertion specification has already been defined and established, while the VME upgrade is still in draft status. Another contributing factor is that in a VME chassis, critical control signals are daisy-chained to propagate down the backplane starting from slot one. The VITA 1.1-1998 VME64 Extensions draft removed many obstacles with the additional live insertion features made available via the 160-pin, 5-row, DIN-style connectors, which include staggered pins providing proper bus signal pre-bias voltage and geographical addressing at the slot level from the P1 connector in system memory space. The basic framework for providing a live insertion system exists when you combine this draft with the VITA 1.4, VME64x Live Insertion System Requirements Draft Standard (VITA 1.4-200x).
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