Virtual Memory and Paging Explained
Learn how physical memory virtualization, page tables, page faults, and thrashing work in modern operating systems.
What is Virtual Memory?
Virtual Memory is a memory management technique that makes physical RAM appear much larger and contiguous by mapping logical address spaces to physical locations (and backing storage swap space).
Benefits of Virtual Memory:
- Isolation: Each process has its own address space, preventing processes from corrupting each other's memory.
- Security: Blocks unauthorized memory access.
- Efficiency: Enables launching processes that require more space than physical RAM.
Understanding Paging and Page Faults
The OS divides virtual memory into fixed-size chunks called pages (usually 4KB) and physical memory into matching chunks called frames.
A Page Table maps virtual pages to physical frames. When a process requests a page that is not currently loaded in physical RAM, the CPU hardware generates a Page Fault interrupt. The OS intercepts the fault, fetches the page from disk swap space, loads it into an empty physical RAM frame, updates the Page Table, and resumes the instruction.
If the system runs extremely low on physical RAM, it spends more time swapping pages in/out of disk than executing instructions. This critical performance drop is called Thrashing.