Legacy System

The term “legacy system” is often used to reference obsolete or "legacy" computer hardware or operating systems. A legacy system is an old computer system or program that continues to be used instead of being replaced. Legacy systems often run on obsolete hardware, (spare parts for such computers become increasingly difficult to obtain).

Over time, a lack of understanding of these systems grows, and the designers of the system may become unavailable. This can be exacerbated by inadequate documentation. Compatibility issues may also pose challenges to the integration process. If such systems still “get the job done,” organizations may have financial reasons for using a legacy system, but the cost of maintaining the system may eventually outweigh the cost of replacing both the software and hardware unless backward compatibility is established.