Operating System - Thrashing and File

Q. Consider the following sequence of memory reference from 460 words programs

10,11,104,170,73,309,185,245,246,434,364

a. give the reference string assuming page size of 100 words

b. find number of page faults using LRU assuming 200 words of primary memory.

Solution.

a.

Reference String assuming 100 words

1,1,2,2,1,4,1,2,3,3,5,5,4

b.

Using LRU

Page size=100 words

Primary memory=200 words

So no. of pages = 200/100=2

Thrashing

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CPU utilization for a process decreases if continuous swapping of memory takes place once the memory is full and there is no place for other program execution(thats where virtualization comes into existence).

File Structure

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1. Single Level File Structure

Example-> C:\>Program files

2. Double Level File Structure

Example-> C:>Program files>Microsoft

Similarly ....Multi level File access has many levels

File Access

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1. Sequential file Access

2. Index Sequential

3. Secondary Sequential

4. Direct File Access

File Allocation Methods

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1.Contiguous File Allocation

2.Linked File Allocation

3.Indexed File Allocation

Indexed File allocation is the most efficient file allocation because :

->direct memory access

->Least memory wastage