Parallel adoption is a method of hardware or software migration that involves using the existing and new systems simultaneously until the implementation is judged to be complete and satisfactory.
During the transition, users work with both systems as they gradually learn the new software. There is generally some duplication of effort as, for example, data must be entered in both systems. That duplication can lead to data quality issues. If the two systems aren’t fully compatible, parallel adoption is not a viable migration method.
Parallel adoption is the most foolproof and user-friendly implementation method. However, it can also be the most time-consuming option and is usually the most expensive. Other software migration models include big bang adoption, phased rollout and pilot conversion.