Definity UN330B

In high and critical-reliability systems with 2 SPEs, 1 UN330B resides in each SPE and connects to the other UN330B. The UN330Bs provide control and communication paths between the SPEs to keep the standby SPE ready to assume control if the active SPE fails. The UN330Bs select active/standby mode for the 2 SPEs, shadow(copy) the active SPE memory writes into the standby SPE memory, and support inter-SPE communications.

The duplication channel is a bi-directional hi-speed path between the 2 SPEs. When Memory shadowing is active, all shadowed memory writes on the active processor's bus are sent across the link and written into the standby processor's memory. Standby memory writes are not sent to the active processor.