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The obvious hint for this question is Concurrency. Both Single processor/shared memory hint that it is better to divide the tasks into multiple processes and let the OS try to execute them in parallel(single CPU will not let that happen). Depending on the tasks they might or might not execute in less than 8 hours.

then take n processors, and divide all these n process of each processors, and execute them parallely, as they are independent jobs, so there wont be any shared data between them. ya but this require you to change your code, make it multi-threaded, but if it is then we don't have to do anything, we just need to add more processors, it would be better if we add n processors(for efficiency), but more or less is also fine.

Basically agree with @Abhi, but can do more about scheduler, like shortest job first, Multi-level Feedback Queue or Rotating Stair Deadline Scheduler, to run CPU-extensive and I/O-extensive tasks separately.

1) Use n different processor
2) Follow up 1 (single processor ): use different process
2) Follow up 2 (shared memory ) : use multiple threads within the same process .