Operating systems Exam Questions

What are two types of low-level operations that higher-level synchronization operations(e.g., semaphores and monitors) can be built upon?
test-and-set. compare-and-swap. atomic reads and writes. Other atomic operations. enabling
and disabling interrupts.
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What is the difference between a process and a thread?
Every process has its own address space, but multiple threads inside a process share part of
the memory with their parent process. There is less context switching overhead to switch
among threads when compared to switching among threads.
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What is the difference between deadlock and starvation?
In a deadlock situation, none of the involved processes can possibly make progress. In a
starvation situation, a process is ready to execute, but it is not being allowed to execute.
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Suppose our computer system is running five processes (P1,P2,P3,--,P5 ) and has four
separate types of resources (A,B,C,D). We want to see if the system is in a safe state
using the Banker's algorithm. Using the following information about the state of the
system, determine if the state is safe: (11 points)
Total
AB C D
4 5 4 3

Available
AB C D
0 1 0 0

Maximum
A B C D
P1 1 3 3 0
P2 2 2 1 3
P3 1 1 0 1
P4 1 4 1 0
P5 3 1 2 1

Used
A B C D
P1 0 1 2 0
P2 2 0 1 1
P3 1 0 0 1
P4 0 3 1 0
P5 1 0 0 1

A B C D
Total 4 5 4 3

A B C D
Available 0 1 0 0

Total gives the number of instances of each resource in the system; Available gives the
number of unallocated instances of each resource; Maximum refers to the maximum
number of instances of each resource required by each process; Used refers to how many instances of each resource each process currently holds.

Answer:
The Need matrix is as follows:
Need
A B C D
P1 1 2 1 0
P2 0 2 0 2
P3 0 1 0 0
P4 1 1 0 0
P5 2 1 2 0

The state of the system is unsafe. Executing the Banker's algorithm terminates with P2
and P5 unable to complete. We give a possible sequence of execution with "Work" P3 runs (1, 1, 0, 1), P4 runs (1, 4, 1, 1),P1 runs (1, 5, 3, 1). Now neither P2
nor P5 can release its resources because each holds resources the other needs.
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2. A computer system has m resources of the same type and n processes share these
resources. Prove or disprove the following statement for the system:
This system is deadlock free if sum of all maximum needs of processes is less than m+n.

3. There are four processes which are going to share nine tape drives. Their current and
maximum number of allocation numbers are as follows :
process current maximum
p1 3 6
p2 1 2
p3 4 9
p4 0 2
a. Is the system in a safe state? Why or why not?
b. Is the system deadlocked? Why or why not?