Parallel Processing Problems
What are the advantages and disadvantages of parallel processing over serial processing? Your answer should begin with a criticism of this question.
This question is flawed in the sense that it does not define the term parallel processing.
Consider a computer with a single core CPU. Does that perform serial processing?
No, it doesn’t. Instruction execution is overlapped (pipelining) and that itself
implements a form of parallelism. Moreover, the various subsystems (display, Ethernet
interface, disk interface, audio controller) will inevitably all have their own embedded
However, this type of question is really asking about the class of parallel processor where the main CPU itself is replicated either as multiple cores on one chip, or multiple processors on one motherboard, or multiple processors in multiple systems.
Parallel processing allows you to divide a problem into parts, allocate individual parts to processors, perform operations in parallel, and then merge the individual results to create the final result. The favorite example of multiprocessing is weather forecasting because you can partition the atmosphere into as many cells as you want and then let a processor work on the climate of its own cell. Parallel processing has become possible because (a) we can do it economically by including multiple CPUs on one silicon chip and (b) we have to do it because we have reached the limit at which we can clock chips and still remove the waste heat.
The problem with parallel computing is that there is no simple way of decomposing
a task into n subtasks. Some problems are very difficult to decompose into individual
tasks and these cannot exploit the hardware of a parallel processor. Moreover, highly
parallel processing requires complex inter-
By how much can we speed up the evaluation of F = a2 + b2 + c2 if addition and subtraction take the same time?
We can’t do any of the additions until at least two squares have been performed. We can carry out the squares in parallel
Step 1: Evaluate a2, b2, and c2 at the same time.
Step 2: We can add a2 + b2 to get a subtotal
Step 3: We can add c2 to the subtotal to get a2 + b2 + c2.
This reduces the number of steps in the serial case from 5 to three, giving a speed up of 5/3 = 1.67.
We could do better if we designed a 3-