Which type of system conversion involves both old and new systems operating simultaneously for a period?

Parallel conversion is the approach where both the old and new systems are run at the same time for a specified period. This method allows users to validate the accuracy and performance of the new system while still relying on the functionality of the old system. Practically, it helps to reduce risks, as any discrepancies or issues with the new system can be addressed without disrupting operations, since users can fall back on the old system if necessary.

During this dual operation, stakeholders can compare outputs from both systems to ensure that the new system is functioning as intended before completely transitioning away from the old system. This method is particularly beneficial in critical environments where system failure can lead to significant consequences.

In contrast, pilot conversion involves implementing the new system in a specific area or department before a full rollout, allowing for focused testing and feedback. Prototyping refers to creating an early model of the system for user evaluation, while agile methods focus on iterative development and continuous feedback but do not specifically pertain to system conversion strategies as described in the question.