legacy system
n.
ComputingSoftware or hardware that was built using methods that are outdated or obsolete.
Notes
'Legacy system' connotes a system that is large and monolithic, and that is difficult to modify because the software is written in a programming language that is no longer common. It is maintained because the costs of converting to a new system do not justify the benefits to an organization. As a legacy system becomes older, the costs of maintenance will likely be greater than the value of the information it contains or greater than the costs of upgrading the system. In the former case, the information is effectively destroyed when the system is decommissioned.
