There are two basic types of scheduler
1. Preemptive
2. Non-preemptive

Preemptive schedulers are based on priority, means if there are tasks of same priority then all tasks will get same time otherwise if higher priority task will arrive it will be processed first.

Whereas in non-preemptive scheduler processes does not scheduled based on priority all tasks will be processed for same amount of time in simple round robin fashion.