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• The CPU tries to access a page
• But the page is not currently in RAM

Steps:

1. OS detects the page fault
2. Finds the page on disk
3. Loads it into a free frame in RAM
4. Updates the page table
5. Execution continues

4.9 Advantages of Virtual Memory

• Programs larger than RAM can run
• Better multiprogramming
• Efficient memory use
• Process isolation and protection

4.9.1 Disadvantages

• Slower than RAM because disk access is slow
• Too many page faults cause Thrashing

4.9.2Thrashing

Thrashing occurs when:

• The system spends more time swapping pages between RAM and disk
• Instead of executing programs

This leads to very poor performance.

4.9.3 Simple Example

Suppose:

• Program size = 10 MB
• RAM available = 4 MB

Virtual memory allows:

• Only 4 MB of the program in RAM
• The rest 6 MB stays on disk
• Pages are loaded only when needed

https://www.youtube.com/watch?v=fGP6VHxqkIM

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