Which implementation method launches a new system while the old one continues to operate for comparison?

Parallel implementation is a method where the new system is launched alongside the existing system, allowing both to operate simultaneously for a certain period. This approach facilitates a direct comparison of the new system's performance against the established one, helping to identify any discrepancies, issues, or advantages of the new system before fully transitioning. It provides a safeguard by ensuring that if the new system encounters problems, the old system remains functional and can be relied upon to maintain operations without disruption.

This method is particularly beneficial as it allows users to gradually acclimate to the new system while still having access to the familiar processes of the old system. Additionally, any data transferred or operations carried out in the new system can be validated against the old system, enhancing confidence in the new implementation.

Other methods like sequential, phased, and direct implementation do not offer this side-by-side operational capability. Sequential implementation typically refers to a method where one process follows another without overlap. Phased implementation involves gradually introducing components or phases of the new system rather than operating both systems together. Direct implementation transitions fully to the new system immediately, without the option to revert to the old if issues arise. Thus, parallel implementation stands out for its comparative assessment and risk mitigation during the transition.