Systems implementation strategies: Which approach runs the old (legacy) system and the new system simultaneously for a defined period to reduce risk during changeover?

Introduction / Context:
Replacing a legacy system is risky. Implementation strategies aim to minimize disruption, ensure data correctness, and build user confidence. One widely taught approach involves operating the old and new systems at the same time to verify outputs and processes before fully retiring the legacy system.

Given Data / Assumptions:

• The organization wants to mitigate go-live risk.
• There is budget and staffing to maintain two environments briefly.
• Outputs from both systems can be reconciled during the overlap.

Concept / Approach:
Parallel implementation runs both systems concurrently, comparing results to detect mismatches. In contrast, direct (big-bang) cuts over instantly, pilot deploys to a limited group/site first, and phased rolls out incrementally by module or region. Parallel provides high assurance at higher cost and effort, suitable for mission-critical or compliance-sensitive processes (e.g., payroll, billing).

Step-by-Step Solution:

Verification / Alternative check:
Implementation plans often include dual-run periods with reconciliation reports to confirm that the new system matches the legacy outputs before final cutover.

Why Other Options Are Wrong:
Direct is high risk; pilot limits scope but not dual-run; phased staggers features or sites but does not require simultaneous operation at full scale.

Common Pitfalls:
Insufficient reconciliation criteria; too short a parallel window to capture rare edge cases; user confusion when two systems co-exist.

Final Answer:
parallel