Which of the following MOST effectively minimizes downtime during system conversions?

The most effective way to minimize downtime during system conversions is to use a parallel run. A parallel run is a method of system conversion where both the old and new systems operate simultaneously for a period of time until the new system is verified to be functioning correctly. Thisreduces the risk of errors, data loss, or system failure during conversion and allows for a smooth transition from one system to another. References: CISA Review Manual, 27th Edition, page 467