The variety of methods used to install a new system, which may include a full cutover (simultaneous implementation of all system functions), phased cutover (implementing a series of modules or subsystems over different periods of time), parallel (simultaneously running both the old and new systems to compare performance and output), and many other variations. The approach depends on the project goals, scope, resources and timeframe available, similarity between old and new systems, number of sites to be implemented, degree of functional integration and many other factors.