Lucent Technologies Inc.

Avaya Technology LLC

John Michael Nichols

Richard Alan Windhausen

Billy G Fuller

David Martin Sueper

Donald G Koch

Alan J Literati

Walter Patrick Christmas

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.

Selective memory duplication arrangement

An arrangement (FIG. 1) that allows banks (15, 25) of up to eight duplicated active devices (30-37, 40-47) to be connected to a SCSI bus (14) and to share SCSI device IDs, and also allows multiple hosts (10, 20) to share the SCSI bus and the connected active devices. Tri-state buffers (200) act as gates (13, 23, 38, 48) to interface host adapters (12, 24) of a plurality of hosts, and active devices of a plurality of device banks, to the SCSI bus. The gate of only one host adapter and the gates of only one bank of devices are enabled at any one time. Only the devices of the enabled bank can receive and respond to addresses from the SCSI bus, while the devices of the other banks are prevented from receiving and responding to addresses from the SCSI bus. Each host has a tri-state buffer acting as bank selector (16, 26) for selecting one of the device banks, by enabling the gates of the devices of the selected bank through a bank select bus (50). Only one host's bank selector is enabled at any one time.

Arrangement for expanding the device capacity of a bus

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Broomfield, CO, United States of America

John Michael Nichols