Unit 1 + Unit 2 + Unit 3

The method of mapping the consecutive memory blocks to consecutive cache blocks is called ______

• Set associative

• Associative

• Direct

• Indirect

Answer explanation

In Direct Mapping, each block of main memory maps to exactly one block in the cache. This is done using the formula:
Cache Block = (Main Memory Block Number) % (Number of Cache Blocks)

It is simple and fast but can lead to conflicts if multiple memory blocks map to the same cache location.

Other types:

• Associative Mapping allows a memory block to go to any cache block.

• Set-Associative Mapping divides the cache into sets, offering a balance between direct and associative mapping.

• Indirect is not a standard cache mapping technique.

Consider the following page reference string. 1 2 3 4 2 1 5 6 2 1 2 3 7 6 3 2 1 2 3 6 For FIFO page replacement algorithms with 3 frames, the number of page faults is?

• 16

• 15

• 14

• 11

Answer explanation

• The FIFO algorithm replaces the oldest page in memory when a new page is referenced and not found in the frames.

• Every time a new page is loaded (not already in memory), it counts as a page fault.

• The total number of page faults in this case is 16.

In which of the below phenomenon, memory is wasted?

• Campaction

• Fragmentation

• Multiplexing

• Paging

• Thrashing

Answer explanation

Fragmentation: When memory is allocated to a huge number of non-contiguous memory chunks and leaves a high amount of unallocated memory but still, that unallocated chunk of memory is unusable then this phenomenon is called fragmentation.

There are two types of fragmentation:

·        Internal Fragmentation: This fragmentation occurs when the allocated partition s occupied by the program of size lesser than the partition. It occurs in fixed-size memory allocation.

 

·        External Fragmentation: This fragmentation occurs when enough contiguous space cannot be found as the empty partitions are dispersed non-contiguously. It occurs in dynamic memory allocation.

To avoid the race condition, the number of processes that may be simultaneously inside their critical section is

• 8

• 1

• 16

• 0

Answer explanation

To avoid race conditions, only one process should be allowed inside its critical section at a time. This ensures mutual exclusion, a key requirement in solving the critical section problem in concurrent programming.

Allowing more than one process in the critical section can lead to inconsistent or incorrect results due to simultaneous access to shared resources.

For a deadlock to arise, which of the following conditions must hold simultaneously?

• Mutual exclusion

• No preemption

• Hold and wait

• All of the mentioned

Answer explanation

A deadlock can occur only if all the following four conditions hold simultaneously:

1. Mutual Exclusion – Only one process can use a resource at a time.

2. Hold and Wait – A process holding at least one resource is waiting to acquire additional resources.

3. No Preemption – A resource can be released only voluntarily by the process holding it.

4. Circular Wait – A set of processes are waiting for each other in a circular chain.

These are known as the Coffman conditions. If even one of these is prevented, deadlock can be avoided.

All unsafe states are ____________

• deadlocks

• not deadlocks

• fatal

• none of the mentioned

Answer explanation

All unsafe states are not necessarily deadlocks. An unsafe state means the system might enter a deadlock if the processes proceed in a certain way. However, it's still possible for the system to avoid deadlock by careful resource allocation.

• Safe state: The system can allocate resources to each process in some order and still avoid deadlock.

• Unsafe state: There is a risk of deadlock, but it has not occurred yet.

• Deadlock: A definite condition where processes are stuck waiting for resources forever.

A system has 12 magnetic tape drives and 3 processes : P0, P1, and P2. Process P0 requires 10 tape drives, P1 requires 4 and P2 requires 9 tape drives.

Which of the following sequence is a safe sequence?

• P0, P1, P2

• P1, P2, P0

• P2, P0, P1

• P1, P0, P2

Answer explanation

Can P1 run?

Yes, P1 needs 2, and we have 3.
→ Run P1, release 2 → Available = 5

Can P0 run now?

Yes, P0 needs 5, and we now have 5.
→ Run P0, release 5 → Available = 10

Can P2 run now?

Yes, P2 needs 7, and we have 10.
→ Run P2, release 2 → Available = 12

✅ Safe Sequence: P1 → P0 → P2

A system has 3 processes sharing 4 resources. If each process needs a maximum of 2 units then, deadlock ____________

• can never occur

• may occur

• has to occur

• none of the mentioned

Answer explanation

To determine whether deadlock can occur, we use the deadlock avoidance principle (specifically the Banker's algorithm safety condition).

Systems that do not have parallel processing capabilities are ______________

• SISD

• MIMD

• SIMD

• MISD

Answer explanation

• SISD (Single Instruction stream, Single Data stream) systems are traditional sequential computers where a single processor executes a single instruction at a time on a single data stream.

• These systems do not support parallel processing.

All nodes in each dimension form a linear array, in the __________.

• Star topology

• Ring topology

• Connect topology

• Mesh topology

Answer explanation

In a mesh topology, particularly in a multi-dimensional mesh, all nodes in each dimension form a linear array. These arrays are interconnected to form a grid-like structure, where each node connects to its adjacent nodes in the respective dimensions.