parallel conversion:
"A project implementation technique in which an existing system is run in parallel with the new system, with the comparison of operations and results to verify that the new system will properly replace the functions of the old. Parallel conversions are often difficult due to the time, expense and viability of operating two systems and problems in comparison and verification when functions have changed significantly. A parallel is often not necessary when the conference room pilot and issue identification and resolution phases are done well, and adequate resources are made available at cutover time. "
