Virtual Memory and Demand Paging
page 1 of 8
Published: 30 Aug 2006
Unedited - Community Contributed
Abstract
Virtual Memory allows a program of larger size than available memory to be loaded and executed by loading the same in parts. Demand Paging refers to loading a page of program code from disk into memory as and when it is required by the program. This article discusses both these concepts in detail.
by Joydip Kanjilal
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Introduction

One of the most important of all concepts related to Memory Management is Virtual Memory.  Virtual Memory refers to the concept whereby a process with a larger size than available memory can be loaded and executed by loading the process in parts.  The program memory is divided into pages and the available physical memory into frames.  If a process attempts to access a page that is not available in the main memory and the information of which does not exist in its page table, a page fault occurs.  The Operating System now takes care of swapping this page in to the main memory from the backing store.  The Operating System follows its predefined algorithms for page replacement.  Demand Paging refers to loading a page of program code from disk into memory as and when it is required by the program.  The region of the backing store that is used to store the swapped out pages from the main memory is called swap space.  This article discusses Virtual Memory with special reference to Demand Paging and sheds light on some the most commonly used page replacement strategies that are adopted by the Operating Systems.


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User Comments

Title: virtual memory and paging concepts   
Name: Suganthi Velusamy
Date: 12/28/2006 1:10:43 AM
Comment:
This is very very useful for me to know about the virtual memory concets and paging concepts clearly. Thanks a lot for you to make me to get a clear idea of what is virtul memory and all of its corresponding operations. Can u please guide me by an article for threading concepts in detailed manner?
Title: Mapping virtual address to physical   
Name: Swetha
Date: 10/15/2006 3:07:27 PM
Comment:
Hello Sir,

The article is very good for beginners like me.But ca you tell me whether can I write a code to map virtual address to physical addres.

Warm Regards
swetha
Title: Suggestion   
Name: Sandeep Acharya
Date: 8/30/2006 12:30:59 PM
Comment:
The article is really good. We all know that covering the paging concept in a small article is very tough. But I guess it could be better if you can throw some more light on the "Pure demand Paging" and how it could "Thrash" an application. I guess a pictorial/graphical explanation could be better. ANyway its a suggestion only. And I am really appriciating the article. Hoping to have some good articles like this in future.

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