A legacy system refers to outdated infrastructure, applications, and processes, "a system that often holds the middle tier of a multiple-tier system" is not a characteristic of this system.
It describes software or IT systems that have been around for a long time and that, from a technological point of view, should be replaced by a more modern version.
A legacy system has often been used for a long time and is no longer technologically up to date, however these old applications are still used for various reasons, for example because they form the basis of newer software.
Therefore, we can conclude that legacy systems are those computer systems that have become outdated but are still used by companies, "a system that often holds the middle tier of a multiple-tier system" is not a characteristic of this system.
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