Shortest Process Next (SPN): Another approach to reducing the bias in favor of long processed inherent in FCFS is the SPN. This is a non-preemptive algorithm in which the process with the shortest expected processing time is selected next. Thus a short process will jump to the head of the queue past longer jobs.
Shortest Remaining Time (SRT): SRT algorithm is a preemptive version of SPN. In this case, the scheduler always chooses the process that has the shortest expected remaining processing time. When a new process joins the ready queue, it may in fact have a shorter remaining time than the currently running process. SRT does not have the bias in favor of long processes found in FCFS.