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Related to legacy system: Legacy software
legacy systemAn obsolete computer system centred around a mainframe platform which is not worth the cost of upgrading or salvaging. As enterprise modernises hardware, IT departments may be forced to integrate legacy system data, which can be logistically difficult, since obsolete software was often custom written by people who left the institution.
legacy system(leg′ă-sē) [L. legatia, office of deputy]
An old, slow, or out-of date computer system.