GATE - 2008 | OS | Match the following flag bits used in the context of virtual memory

GATE - 2008 | OS | Match the following flag bits used in the context of virtual memory
Posted on 15-02-2022

GATE - 2008 [Operating System]

Question:

Match the following flag bits used in the context of virtual memory management on the left side with the different purposes on the right side of the table below.   

GATE - 2008

A

I-d, II-a, III-b, IV-c

B

I-b, II-c, III-a, IV-d

C

I-c, II-d, III-a, IV-b

D

I-b, II-c, III-d, IV-a

      

Solution:

Option (D) is Correct.

Dirty bit:
The bit indicates that its associated block of memory has been modified and has not been saved to storage yet. Dirty bits are used by the CPU cache and in the page replacement algorithms of an operating system.


R/W bit:
If the bit is set, the page is read/ write. Otherwise when it is not set, the page is read only.


Reference bit:
Reference bit is used in a version of FIFO called second chance policy, in order to avoid replacement of heavily used page.


Valid bit:
Valid bit is not used for page replacement. It is not used in any page replacement policy. It tells the page in the memory is valid or not. If it is valid it is directly used and if it is not then a fresh page is loaded.

So, basically it is page initialization, because we are not replacing, it is initializing, we not knocking out somebody, we are filling empty space. So initialization and so option (D).

Thank You

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