A system, such as a software application, that is out of date, usually because it exists on an older technology stack. Legacy systems pose a number of problems to organizations; for example:
- the hardware or software they run on may no longer be supported by the original supplier
- staff that understands the systems may have retired from or left the organization
- integration with newer software may be difficult or impossible
- documentation may no longer exist
- they may expose an organization to security breaches
Despite myriad problems caused by legacy applications, there are reasons why they continue to exist in organizations. These systems tend to have a good track record of running smoothly, sometimes continuously, with minimal problem. They may contain complex business logic that does not exist and is not documented elsewhere. Perhaps the most common reason is that there is simply no incentive for an organization to spend time and money to rewrite the application in a new technology.