Replacement policy
Beginner
The rule a cache uses to pick which block to throw out when it needs room.
Novice
How a cache chooses the victim when a set is full: least recently used (LRU), an approximation such as tree pseudo-LRU, first-in first-out, or random.
Expert
True LRU needs log2(N!) bits per N-way set, so hardware uses tree PLRU or not-recently-used bits; last-level caches use scan- and thrash-resistant policies such as RRIP that predict re-reference distance.