5d - Changeover methods

5d - Changeover methods

1. Parallel

   • The old system continues to run while the new system is installed
   • When theere is confidence in the new system, the old system is retired
   • Advantages
     • Accuracy of new system can be compared with legacy system
     • Suitable for life/mission crtical systems
     • Can revert to old system if there is a problem
   • Disadvantages
     • All work is duplicated
     • May not have spacce for 2 sets of physical equipment
     • May result in data integrity issues

2. Phased

   • Parts of a system are introduced one at a time
   • Can be combined with all other methods
   • Advantages
     • Training can be staggered
     • Low risk as only part of the system may fail
     • Errors can be corrected with little effect on the rest of the system
   • Disadvantages
     • Old and new systems may not be compatible
     • Can take a long time to implement
     • Can be confusing 2 different systems at the same time

3. Pilot

   • The system is trialled with a group or department
   • Can be combined with all other methods
   • Advantages
     • Training can be cascaded
     • Errors can be corrected before main group go live date
     • Low risk as only small group are affected by failure
   • Disadvantages
     • Can take a long time to implement
     • Staff may feel like 'guinea pigs'
     • Old and new system may not be compatible

4. Direct

   • The new system takes over from the old system immediately
   • The old system is retired immediately
   • Advantages
     • Can be implemented during non-busy times
     • Cheap to implement as no duplication of work
     • No risk of data integrity due to duplication
   • Disadvantage
     • Problems could lead to system failure
     • All training must be completed in advance
     • Nothing to fall back on