Chapter 10: Virtual Memory: Demand Paging, Page Replacement, and Thrashing

Virtual Memory: Demand Paging, Page Replacement, and Thrashing begins by explaining the benefits of virtual memory, including program size flexibility, increased multiprogramming, and separation of logical from physical address spaces. The chapter introduces demand paging, describing how page faults occur and how the operating system uses a valid–invalid bit and page-replacement algorithms to manage memory efficiently. Detailed coverage is given to page replacement strategies, including FIFO, optimal, LRU (Least Recently Used), and second-chance algorithms, along with the concept of the working set model to reduce thrashing. The discussion extends to frame allocation policies, global versus local replacement, and load control techniques. It also examines memory-mapped files for I/O optimization and the role of copy-on-write in process creation. The chapter addresses performance considerations, such as effective access time, and hardware support for virtual memory through translation look-aside buffers (TLBs). Real-world implementations in systems like Windows and Linux are provided to show how these concepts are applied. By the end, readers understand how virtual memory improves flexibility, efficiency, and security in modern computing environments while balancing performance trade-offs.