A scheduler is a type of system software that allows you to handle process scheduling.
There are mainly three types of Process Schedulers: Long Term, Short Term, Medium Term. These are explained as following below.
- Long Term or job scheduler :
Long term scheduler is also known as job scheduler. It chooses the processes from the pool (secondary memory) and keeps them in the ready queue maintained in the primary memory.Long Term scheduler mainly controls the degree of Multiprogramming. The purpose of long term scheduler is to choose a perfect mix of IO bound and CPU bound processes among the jobs present in the pool.
- Short term or CPU scheduler :
Short term scheduling is also known as CPU scheduler. The main goal of this scheduler is to boost the system performance according to set criteria. This helps you to select from a group of processes that are ready to execute and allocates CPU to one of them. The dispatcher gives control of the CPU to the process selected by the short term scheduler. - Medium-term scheduler :
It is responsible for suspending and resuming the process. It mainly does swapping (moving processes from main memory to disk and vice versa). Swapping may be necessary to improve the process mix or because a change in memory requirements has over committed available memory, requiring memory to be freed up.
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