Which implementation method is least suitable for replacing an existing legacy system under time pressure?

Choosing the direct changeover method for replacing an existing legacy system under time pressure is least suitable due to the inherent risks and challenges associated with this approach. Direct changeover, also known as "big bang," involves transitioning from the old system to the new system all at once. This method means that once the new system is implemented, the old system is completely shut down.

In a time-sensitive situation, the concerns primarily arise from the fact that if the new system fails to perform as expected or if there are unforeseen issues, the organization has no fallback option. There's no running of both systems in parallel, which could provide a safety net. Additionally, direct changeover requires exceptionally thorough preparation and confidence in the new system's functionality, which may not be possible under strict time constraints. There may not be adequate time for comprehensive testing or training users on the new system, increasing the risk of disruption to operations.

In contrast, methods like parallel running, where both systems operate simultaneously for a period, allow for comparison and serve as a safeguard against potential problems of the new system, making it more suitable in pressured situations. Options such as phased implementation or pilot approaches also typically involve gradual changes, allowing for adjustment and problem-solving along the way, thereby reducing risk and providing