Memory

Question 1

What are the two main types of shared memory?

Answer 1

1. Uniform Memory Access
2. Non-Uniform Memory Access (NUMA)

Question 2

What is SMP?

Answer 2

Symmetric Multiprocessing OR Shared-Memory Multiprocessing : computer processing done by multiple processors that share a common operating system (OS) and memory.

Question 3

Give 3 advantages of using a shared memory system.

Answer 3

1. User-friendly programming - easy access of variables.
2. Fast and uniform data sharing can be obtained.
3. Better performance for small systems with 10-100 processors.

Question 4

Give 2 disadvantages of using a shared memory system.

Answer 4

1. Scalability is difficult and costly.
2. Programmer must ensure correct access to global memory by using synchronization constructs to prevent non-deterministic conditions, etc.

Question 5

Give 3 advantages of using a distributed memory system.

Answer 5

1. Easier for scalability –> processors are directly proportional to memory.
2. Cost effective.
3. Preferred for larger systems of 100-1000 processors.

Question 6

Give 2 disadvantages of using a distributed memory system.

Answer 6

1. Data communication between processors is difficult –> programmer should handle it.
2. Time for accessing memory will not be uniform.

Question 7

What is the difference between shared memory and distributed memory?

Answer 7

• In shared memory the processors have a shared global address space that is accessible to all N processors.
• In distributed memory each processor has a private/local memory.

Question 8

Draw diagrams of each of the 4 parallel machines.

Answer 8

<draw>
1. SISD
2. SIMD - global clock to sync lockstep
3. MISD
4. MIMD
</draw>

Question 9

List the 4 memory access models in shared memory computers

Answer 9

1. EREW
2. ERCW
3. CREW
4. CRCW

Question 10

Calculate the time complexity of a parallel array sum program for each of the shared memory access models.

Answer 10

• do. - slides–> L03-18

Question 11

List 5 methods used for conflict resolution in shared memory computers and explain each.

Answer 11

1. Arbitrary choice - select a write value from one processor randomly or based on a priority.
2. Priority - select value based on priority value assigned to processor.
3. Sum - sum of all values from all processors.
4. Min/Max - select the min/max of all values
5. Common value - only update if all values from all processors requesting to write are the same.