Basic CS-Operating System [3i Infotech Placement]: Sample Questions 51 - 51 of 89

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Question 51

Operating System
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Describe in Detail

Essay▾

What are demand-and pre-paging?

Explanation

Demand-Paging

Diagram of Demand Paging
  • The transfer of page from secondary memory to primary memory is upon need- that is “on demand” - page brought into memory when a location on page is referenced during execution.
  • Process begins execution with no page in physical memory- page faults accrue the process՚s working set in physical memory.

Advantages of bringing a page into memory only when needed:

  • Less I/O needed
  • Faster response
  • Support for more users
  • Loading pages of memory on demand lowers the memory footprint.
    • Memory footprint refers to amount of main memory that a program uses or reference while running.

Pre-Paging

Understanding of Pre-Paging
  • Tries to predict which page would be required next by the processor and brings that proactively into memory.
  • Assumes for example that process requests consecutive address and gets the next page when last address on this page is accessed. Actual prediction schemes might be more complicated.
  • Retrieval of a page other than demanded by a page fault hoping that additional page would be needed in future.

Advantages and Disadvantages of Pre-paging

  • If pre-paged page are unused , I/O and memory are wasted.
  • Good strategies to pre-page might however increase the performance by reducing expensive page faults.

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