Operating Systemsmedium

Explain virtual memory and paging.

Tags

#virtual-memory#paging#performance

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Answer

Virtual memory gives each process its own address space mapped to physical memory. Paging moves fixed-size pages between RAM and disk, enabling isolation and larger memory than RAM.

Advanced answer

Deep dive

VM provides isolation and flexibility:

Page tables map virtual to physical addresses.
Page faults occur when a page is not in RAM.
The OS uses replacement policies (e.g., LRU approximations).
Too many faults cause thrashing and severe slowdown.

Examples

Page fault flow:

Access page -> fault -> load from disk -> update page table -> resume

Common pitfalls

Assuming swap is “free memory.”
Ignoring working set size (thrashing).
Overcommitting memory without monitoring.

Interview follow-ups

What is the working set of a process?
How does copy-on-write use paging?
How do huge pages affect performance?

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