Running parallel (also called parallel operation) refers to using both the old (legacy) and new software or system concurrently for a specified period of time in order to test the new system. The old system is assumed to be the “production” system of record, while the new, replacement system is assumed to be in a “development”, non-production status.
During parallel operation, both systems operate concurrently, support the same functions, process the same data, and are expected to produce the same result. Data entry and workflow are duplicated and discrepancies between the expected results are reconciled and appropriate follow-up action taken. There is an assumption that when the replacement system has satisfied established test performance criteria and results, the old system will be phased out or discontinued and the replacement system will be migrated to “production” status and become the new system of record.