briefly describe about virtual memory. what is virtual memory? advantage of virtual memory disadvantage of virtual memory needs of virtual memory LRU FIFO OPT FIFO ALGORITHM LRU ALGORITHM OPT ALGORITHM PAGE REPLACEMENT ALGORITHM

1. Present by :-
Ritul De

2. CONTENTS
 Introduction
 Advantages of Virtual Memory
 Disadvantage ofVirtual Memory
 FIFO
 LRU
 Page Replacement Algorithms
 OPT

3. Introduction
 Virtual memory is a separation of user logical memory from physical
memory.
 In this method, we keep only a part of the process in the memory and other
part on the disk (secondary storage)

4.  Only part of the program needs to be in memory for execution.
 Logical address space is much larger than physical address space.
 Need to allow pages to be swapped in and out.
 Virtual memory allows speed gain when only a particular segment of the program
is required for the execution of the program.
 This concept is very helpful in implementing multiprogramming environment.

5.  Applications run slower if the system is using virtual memory.
 ItTakes more time to switch between applications.
 Less hard drive space for your use.
 It reduces system stability.

6.  It is the technique used by operating system to decide which
memory pages swap out .
 It is also decided that is memory , how much frames to allocate
to each process.

7. First In First Out (FIFO) Algorithm
 Very simple to implement
 Oldest page is replaced for replacement
 Performance is not always good
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8.  Page which has not been used for the longest time in main
memory the one which will be selected for replacement.
 It is like optimal page-replacement algorithm looking backwards
in time.
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9.  Looks for page in future
 Lowest page fault
 Difficult to implement
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