Virtual Memory

Topics: Virtual memory, Page table, Memory management Pages: 12 (3383 words) Published: July 23, 2013
RESEARCH PAPER ON VIRTUAL MEMORY

Submitted To: Dr. C. Taylor Submitted By: Sumit Sehgal Date: February 3, 2003

Sumit Sehgal

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CONTENTS
INTRODUCTION............................................................................................................... 3 HISTORY ........................................................................................................................... 3 CONCEPTS AND IMPLEMENTATIONS OF VIRTUAL MEMORY ............................ 4 Implementations of Virtual Memory............................................................................... 5 Demand Paging........................................................................................................... 5 Demand Segmentation................................................................................................. 8 Page Replacement ..................................................................................................... 10 ALGORITHMS USED IN VIRTUAL MEMORY .......................................................... 11 First in, first out (FIFO)................................................................................................. 11 Least-recently-used (LRU)............................................................................................ 13 VIRTUAL MEMORY IMPLEMENTATION IN WINDOWS NT ................................. 13 Address Translation....................................................................................................... 14 Windows NT Paging Database ..................................................................................... 15 Virtual Memory Manager.............................................................................................. 17 CONCLUSION ................................................................................................................. 18 BIBLIOGRAPHY ............................................................................................................. 19

Sumit Sehgal

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INTRODUCTION
In today’s world, computers have become an integral and inseparable part of our lives. We use them for many different things in many different ways. However, what is the reason for accepting them so much in our lives? The answer is that computers make our job easier and more efficient. Sometimes, it can be very frustrating or stressful to work with computers that don’t run as fast as we want them to or they just cannot handle certain processes due to shortage of system resources. When the limitations of the system resources become a major barrier in achieving our maximum productivity, we often consider the apparent ways of upgrading the system, such as switching to a faster CPU, adding more physical memory (RAM), installing utility programs, and so on. This process of making sure that the operating system uses its resources most efficiently is called System Optimization. To facilitate the process of system optimization, the concept of Virtual Memory was introduced. A virtual memory system combines paging with automatic swapping. It uses an imaginary storage area (virtual address space) in conjunction with the existing hardware. This allows a program to use a virtual address space that is larger than the physical memory. Along with the ability to execute a process that is not completely in memory, another advantage of this system includes increased multiprogramming feasibility.

HISTORY
The first virtual memory machine was developed in 1959. It was called the one level storage system. Although it was heavily criticized, it spurred many new prototypes during the early 1960's. Before virtual memory could be regarded as a stable entity, many models, experiments, and theories were developed to overcome the numerous problems

Sumit Sehgal

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that were associated with it. Specialized hardware was developed that would take a "virtual" address and translate it into an actual physical address in memory (secondary or...

Bibliography: 1) Silberschatz, Abraham, and Galvin, Peter Baer. Operating Systems Concepts, Sixth Edition. New York: John Wiley and Sons.
2) Virtual Memroy Tutorial. http://cne.gmu.edu/modules/vm/ 3) http://www.cs.duke.edu/~narten/110/nachos/main/node34.html 4) Virtual Memory and Paging http://www.caa.lcs.mit.edu/~devadas/6.004/Lectures/lect19/
5) Windows NT Virtual Memory http://www.osr.com/ntinsider/1998/Virtualmem1/virtualmem1.htm 6) Virtual Memory: Issues of Implementation http://dlib.computer.org/co/books/co1998/pdf/r6033.pdf 7) A Virtual Memory Model for Parallel SupercomputerS”, Proceedings of the 10th International Parallel Processing Symposium (IPPS '96) 1063-7133/96 $10.00 © 1996 IEEE http://dlib.computer.org/conferen/ipps/7255/pdf/72550537.pdf 8) Lister, A.M. Fundamentals of Operating Systems. The Macmillan Press LTD, New York, 1980. 9) Milenkovic, Milan. Operating System Concepts and Design. McGraw-Hill Book Company, New York, 1987. 10) Kath, Randy. December 21, 1992. The Virtual-Memory Manager in Windows NT. http://msdn.microsoft.com/library/techart/msdn_ntvmm.htm 11) Solomen, David A. 1998. Inside Windows NT, 2nd Edition. Microsoft Press, Redmond, WA: pages 217-304.
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