Avaya Technology LLC

Walter Patrick Christmas

Billy G Fuller

Donald G Koch

John Michael Nichols

An active-standby dual processor (,) performs only selective memory duplication and does so via hardware (,) and the operating system (,). A page table (,) stores a shadowing flag (,) for each memory page of the active memory (,) of the processor (,) that indicates whether or not the corresponding page is shadowed. When the operating system allocates (,) memory to a process&mdash;either statically at creation of the process or dynamically during execution of the process&mdash;it checks (,) whether the process program's data statement indicates shadowing or whether the MALLOC request includes a segment selector that indicates shadowing; if so, it sets (,) the allocated page's shadowing flag. When the active processor performs (,) a write of its memory, a page table controller (,) checks (,) if the written page's shadowing flag is set. If so, an interprocessor interface (,) is caused (,) to replicate the write on the standby processor's memory; if not, the write is not replicated.

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Walter Patrick Christmas