Parallel Running for Safer System Modernization

Parallel running matters because the highest-risk point in modernization is often the production cutover, where test assumptions meet live data, users, and business impact. The article explains how legacy and new systems can process the same transactions in parallel, how output comparison exposes discrepancies before decommissioning, and why data consistency, discrepancy resolution, and exit criteria determine whether the approach works. It also clarifies when the added operational cost is justified, particularly for systems where continuity, accuracy, or regulatory confidence is critical. Leaders should treat parallel running as a governed validation program, not an informal safety net.