CS and IT GATE 2020 Questions with Answer

Ques 53 Operating System

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Consider the following five disk five disk access requests of the form (request id, cylinder number) that are present in the disk scheduler queue at a given time.

Assume the head is positioned at cylinder 100. The scheduler follows Shortest Seek Time First scheduling to service the requests. Which one of the following statements is FALSE ?

A

T is serviced before P.

B

Q is serviced after S, but before T.

C

The head reverses its direction of movement between servicing of Q and P.

D

R is serviced before P.

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Ques 54 Operating System

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Each of a set of n processes executes the following code using two semaphores a and b initialized to 1 and 0, respectively. Assume that count is a shared variable initialized to 0 and not used in CODE SECTION P.

CODE SECTION P
wait(a); count=count+1;
if (count==n) signal (b);
signal (a): wait (b) ; signal (b);
CODE SECTION Q

What does the code achieve ?

A

It ensures that no process executes CODE SECTION Q before every process has finished CODE SECTION P.

B

It ensures that two processes are in CODE SECTION Q at any time.

C

It ensures that all processes execute CODE SECTION P mutually exclusively.

D

It ensures that at most n−1 processes are in CODE SECTION P at any time.

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Ques 55 Operating System

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Consider the following statements about process state transitions for a system using preemptive scheduling.

I. A running process can move to ready state.
II. A ready process can move to running state.
III. A blocked process can move to running state.
IV. A blocked process can move to ready state.
Which of the above statements are TRUE ?

A

I, II, and III only

B

II and III only

C

I, II, and IV only

D

I, II, III and IV only

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Ques 56 Operating System

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Consider allocation of memory to a new process. Assume that none of the existing holes in the memory will exactly fit the process’s memory requirement. Hence, a new hole of smaller size will be created if allocation is made in any of the existing holes. Which one of the following statement is TRUE ?

A

The hole created by first fit is always larger than the hole created by next fit.

B

The hole created by worst fit is always larger than the hole created by first fit.

C

The hole created by best fit is never larger than the hole created by first fit.

D

The hole created by next fit is never larger than the hole created by best fit.

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Ques 57 Operating System

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Consider a paging system that uses 1-level page table residing in main memory and a TLB for address translation. Each main memory access takes 100 ns and TLB lookup takes 20 ns. Each page transfer to/from the disk takes 5000 ns. Assume that the TLB hit ratio is 95%, page fault rate is 10%. Assume that for 20% of the total page faults, a dirty page has to be written back to disk before the required page is read from disk. TLB update time is negligible. The average memory access time in ns (round off to 1 decimal places) is ___________ .

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