Virtual Memory and Demand Paging
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by Joydip Kanjilal
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Advantages and Disadvantages of Virtual Memory Systems

The primary advantage or objective of Virtual Memory systems is the ability to load and execute a process that requires a larger amount of memory than what is available by loading the process in parts and then executing them.  The disadvantage is that Virtual Memory systems tend to be slow and require additional support from the system's hardware for address translations.  It can be said that the execution speed of a process in a Virtual Memory system can equal, but never exceed, the execution speed of the same process with Virtual Memory turned off.  Hence, we do not have an advantage with respect to the execution speed of the process.  The advantage lies in the ability of the system to eliminate external fragmentation.  The other disadvantage of Virtual Memory systems is the possibility of Thrashing due to excessive Paging and Page faults.  In may be noted that Trash Point is a point after which the execution of a process comes to a halt; the system is busier paging pages in and out of the memory than executing them.

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User Comments

Title: virtual memory and paging concepts   
Name: Suganthi Velusamy
Date: 2006-12-28 1:10:43 AM
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: 2006-10-15 3:07:27 PM
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
Title: Suggestion   
Name: Sandeep Acharya
Date: 2006-08-30 12:30:59 PM
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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