External Time Reference (ETR)

External Time Reference hardware facility (ETR) is the generic name for IBM Sysplex Timer.

The ETR architecture provides the means of synchronizing TOD clocks in different CPCs with a centralized time reference, which in turn can be set accurately on the basis of UTC time standard (External Time Source). The architecture defines a time-signal protocol and a distribution network (called the ETR network) that permits accurate setting, maintenance, and consistency of TOD clocks.


CPC – Central Processor Complex

TOD – Time of Day

UTC – Coordinated Universal Time

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