System Change over is the process of putting the new information system online and retiring the old system. Change over can be rapid, slow depending on the method we are using. There are four methods used in changing information from old system to new system.
They are:
1) Direct Cutover (it is like throwing switch that instantly change over from old system to new system)
2) Parallel Operation( it require both systems run simultaneously for a specified period)
3) Pilot operation
4) Phased Operation
Direct cutover:
This approach causes the changeover from the old system to the new system immediately when the new system became operational.
Advantages:
1) This system is least expensive
2) It is the most significant approach to use
Disadvantages:
1) It is has more risk than other change over methods regardless how carefully you conduct testing and training.
2) It can result from data situations that were not tested or anticipated
3) Live data typically occurs in much larger volumes than test data.
4) Detecting minor errors are more difficult
5) Users can not verify current output by comparing it to output from old system
6) Major errors can cause system process to terminate abnormally
7) It can not support to revert to the old system as a backup option
Parallel operation:
This change over method requires that both the old and the new information system operate fully for a specific time period. Data input into both system and output generated by the new system is compared with the equivalent output from old system.
Advantages:
1) This method has lower risk
2) If new system doesn’t work correctly then the company can use the old system. as a back up until appropriate changes are made.
3) It is much easier to verify to variety that the new system is working properly under parallel operation
4) Output from both systems can be compared and verified during parallel operation.
Disadvantages:
1) It is the most costly change over method
2) Users must work in both system and the company might need temporary employee to handle the extra work load.
3) Running both systems might place a burden on operating environment and cause processing delays.
4) Parallel operation is not practical if the new system is incompatible technically or if the operating environment can not support both systems.
5) Parallel operation also in appropriate when the two systems perform different functions
Pilot Operation:
Pilot Operation is the method which involves implementing complete new system in a selected location of the company
Advantages:
1) During pilot operation the old system continues t operate for the entire organization including pilot site.
2) It is a combination of parallel operation and direct cutover methods
3) This system reduce the risk of system failure when compared with other methods
4) It is a less expensive
5) This change over period can be much shorter if the system process successful at the pilot site.
Phased Operation:
The phased operation change over method is a process which allows to implement the new system in stages.
Advantages:
1) The risk of errors or failures is limited at implemented modules only.
2) It is less expensive
Disadvantages:
1) This system can not be separated easily into logical modules or segments.
2) If the system involves a large number of separate phases phased operation can cost more than a pilot approach.
