For virtual memory systems using some sort of paging, a policy for which page to replace to make room for other pages is needed. This video covers the First-In-First-Out (FIFO) policy, the Least-Recently-Used (LRU) policy, the standard Clock policy, and also discusses the Optimal policy which is not something that can be implemented in practice, but provides a useful point of comparison. Much of this material is based on content from the book Operating Systems: Internals and Design Principles by William Stallings.