What is virtual memory and how does it work?
This question probes your understanding of memory abstraction and management techniques used to extend physical RAM. It is a core concept in operating system design.
Why Interviewers Ask This
Virtual memory is fundamental to running large applications on limited hardware. Interviewers check if you understand paging, segmentation, and the role of the MMU. This knowledge helps in debugging memory leaks and optimizing application performance.
How to Answer This Question
Define virtual memory as an abstraction layer separating logical from physical addresses. Explain paging and page tables. Discuss demand paging and page replacement algorithms like LRU. Mention the benefits: larger address space and isolation. Briefly touch upon thrashing and how to avoid it.
Key Points to Cover
- Logical vs physical addressing
- Paging and page tables
- Demand paging mechanism
- Page replacement strategies
Sample Answer
Virtual memory allows an OS to use disk space as an extension of physical RAM, creating a larger logical address space. It works through paging, where memory is divided into fixed-size blocks called pages. The Memory Management Unit (MMU) translates virtual addresses to physical ones using page tables. Demand paging loads pages only when needed, improving efficiency. Page replacement algorithms like LRU manage evictions when RAM is full, preventing thrashing and ensuring smooth operation.
Common Mistakes to Avoid
- Confusing virtual memory with swap space
- Missing the role of MMU
- Not explaining page faults
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