GATE CSE 1991 | Question: 03-xi

Question

Indicate all the false statements from the statements given below:

• A. The amount of virtual memory available is limited by the availability of the secondary memory
• B. Any implementation of a critical section requires the use of an indivisible machine- instruction ,such as test-and-set.
• C. The use of monitors ensure that no dead-locks will be caused .
• D. The LRU page-replacement policy may cause thrashing for some type of programs.
• E. The best fit techniques for memory allocation ensures that memory will never be fragmented.

Comments

if u consider the sequence like 12341234......... assume no of frames is 3 then here every page results page fault in LRU It leads to lot of page movements so it causes thrashing

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Option b is true. Peterson solution cannot guarantee mutual exclusion. This line is mentioned in Galvin itself. In fact without the use of atomic instruction synchronization cannot be guaranteed.

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A is True because, the size of virtual storage is limited by the addressing scheme of the computer system and by the amount of secondary memory available. 

ref: see slide-1 in https://home.adelphi.edu/~siegfried/cs553/553l8.pdf

Answer 1

• A. True.
• B. This is false. Example:- Peterson's solution is a purely software-based solution without the use of hardware.https://en.wikipedia.org/wiki/Peterson's_algorithm
• C. False. Reference: https://en.wikipedia.org/wiki/Monitor_(synchronization)
• D. True. This will happen if the page getting replaced is immediately referred to in the next cycle.
• E. False. Memory can get fragmented with the best fit.

Comments

C should be true

Since Monitors have an important property that only one process can be active in the monitor at any time. This will guarantee Mutual Exclusion and hence prevent inconsistency and deadlock.

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Option A is TRUE , Kindly see this blog

https://docs.microsoft.com/en-us/archive/blogs/ericlippert/out-of-memory-does-not-refer-to-physical-memory

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is there a typo in E “Memory can get fragmented with First fit.”, should it be best fit as best fit is asked the question

Answer 2

before answering some points to know:-

• Monitor is one of the ways to achieve Process synchronization. Monitor is supported by programming languages to achieve mutual exclusion between processes.
• Peterson's solution is the purely software-based solution without the use of hardware.
   
• if u consider the sequence like 12341234......... assume no of frames is 3 then here every page results page fault in LRU It leads to a lot of page movements so it causes thrashing
• now go and see selected answer 

Comments

is test and set  is it hardware implementation

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Yes test and set is a hardware approach

Answer 3

A is true as amount of virtual memory is limited by length of MAR and available secondary storage.

D is false as best fit technique causes internal fragmentation.

Not sure about B and C.

Comments

"Best fit" is an algo to find the "holes" ( empty space) in Dynamic Partitioning . Dynamic Partitioning does not cause Internal Fragmentation. External Fragmentation is possible 

Answer 4

a) True.Link

b)False

c)

d)In any replacement policy thrashing could happen, but it mainly causes in time sharing system

thrashing

e) False. It minimize fragmentation onlyLink

Comments

@srestha in best fit there will be external fragmentation right

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Please explain option c!!!

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B should be TRUE.