Legacy systems have a few pros and cons, the ideal response is to evaluate the cost/benefit review, and availability for changes
Issues to evaluate
- Is this a specialized 3rd party product/hardware (may be restricted to vendor eg. ATM's were for a long time OS/2 well after IBM ceased producing OS/2).
- If it is 3rd party, do they still exist, or is there a similar product available.
- Is there specialized hardware requirements. (you may have no problem with a video card, but you might have a problem finding hardware for Wind tunnel Data collection)
- Has the amount of data processing increased/decreased.
- Is the service being utilized less and less.
- Do you have the manpower to handle the existing infrastructure for the proposed life expectancy of the product (if there are 3 people in the world that knows the system, and they all disappear, you may have a problem maintaining the system.
- Will a prolonged outage caused by system being unavailable due to the age, cause a serious impact.
- Is there a good justification that the changes will out weight the current value.
- business logic have been captured, and generated
- system has been optimized for the task
- known output
- Skilled labour, the languages, or hardware may not have limited and aging employee pools. (FORTRAN and COBOL are good examples)
- Increasing costs, technical people and/or parts become more difficult and costly to obtain. Some replacements may have to be custom made even
- Existing hardware could be slower
- Unsupportable protocols (eg SNA or Banyan Vines)
- Security, system may not have been patched for weeks, months or even years.