It's not that it's a ring array; it's that it's a fixed-size ring array with an eviction algorithm, and specifically one that holds representations of entities, where the entity is considered to be destroyed in a semantic sense if it gets evicted from the ring array.

Picture a background jobs system like Sidekik/Resque. Imagine that one worker-node of this jobs system had a fixed-size ring array of jobs it had taken. Now imagine that you could push new jobs onto a specific node. And now imagine that the worker-node responded by not just overwriting one of the filled slots of the local jobs set, but actually ACKing said job to drop it from the global job-queue system. It's destroying a real entity with persistent global identity, in order to reclaim the slot that the local representation of that entity takes up.

That's what OAM is, when combined with the design pattern I'm talking about. It's a ridiculous system that'd never fly in a business; but it happens to work for games, where you control the world such that you can make the world hold "reminders" for the state you destroyed.