legacy system

An old or outdated computer system that remains in use even after more modern technology has been installed, usually because a company has invested considerable time and money into it and it still holds valuable data. A legacy system may also be an entrenched data management platform that contains proprietary, custom-designed software. Fortunately, new software products are designed to work with legacy systems (or at least to import data from them).

A typical legacy system is a database management system (DBMS) running on mainframes or minicomputers (versus new technology solutions, which continue to move to PC-based systems).