Central agent is the Oracle Management Agent that is deployed by default with the first Oracle Management Service.

Oracle strongly recommends that you maintain the agent base directory outside the middleware home, although you can choose to maintain it inside the middleware home. Each Enterprise Manager upgrade is an out-of-place upgrade that results in a new middleware home created for the upgraded release. By maintaining the agent base directory outside the middleware home, you do not have any dependency on the previous release's middleware home, and therefore, you can conveniently delete the previous release's middleware home when it is not needed.

Therefore, when you install a new 24ai Release 1 OMS, you will see the agent base directory created outside the middleware home by default (unless you chose to maintain it inside the middleware home). Similarly, when you upgrade to 24ai Release 1, you will see the agent base directory upgraded outside the middleware home by default (unless you chose to maintain it inside the middleware home in the previous releases).

However, in some cases when you upgrade from older Enterprise Manager versions, you will continue to see the agent base directory inside the middleware home (unless you had already migrated it outside the middleware home). You can choose to migrate the agent base directory to a location outside the middleware if you want.

Note that moving the agent base directory of a central agent outside the Oracle Middleware home is a one-time activity. Once the agent base directory of a central agent is moved outside the middleware home, it remains at the same location even after subsequent upgrades.