Question

I understand that CPU scheduling algorithms are classified into

1. Interactive – Round Robin, Priority scheduling
2. Batch Scheduling – FCFS,SJF

But I cant understand the reason behind the naming Interactive and Batch Scheduling..??
Why are algorithms like RR called interactive and those like FCFS called batch scheduling??

Thanks in advance…

Answer 1

The idea of Batch Scheduling is that there will be no change in the schedule during runtime: a process is scheduled to do an operation on data, and it runs until the process is finished. In ‘interactive’ scheduling, a new process could be launched while another process is running, and so time would be allocated for that process as well as the other. In batch scheduling the schedule is determined at the beginning of the operation.

Example of priority (interactive) scheduling:

Process A has a high priority, and process B has a low priority. Process A runs until it requires some input from the user. While A is waiting, the CPU gives some time to process B. Once the input for A has been gathered, process B is swapped out and process A is given the CPU, due to its higher priority.

Example of batch (FCFS) scheduling:

Process A and process B are processes to be scheduled. Process A is given to the CPU first, so B will not receive any time until A finishes running. Even if A pauses for user input, B will not run (and the CPU time while waiting for input is effectively wasted).

Of course, as with everything this low-level, it’s not entirely that simple: to gain the illusion of multi-tasking, time is generally divided up between processes even when nothing is waiting for I/O. In priority scheduling, this may mean that more time slices are given to A than B while both are running so that A executes quicker. Both interactive and batch scheduling have their pros and cons: while interactive scheduling gives a quicker response time to the user and divides time up more ‘fairly’, an overhead is incurred due to how long a ‘context switch’ takes, which is the time taken for the processor to switch from working on process A to process B.