SJN

SJN is an acronym most commonly used in computer science to denote the Shortest Job Next scheduling algorithm. In its standard form, SJN is a non-preemptive CPU scheduling policy that selects the waiting process with the smallest estimated CPU burst time to execute next. When all processes are available at the same time, SJN can reduce average waiting time and turnaround time compared with longer jobs, making it a useful theoretical model for analyzing scheduling behavior.

SJN is often described as a variant of the Shortest Job First (SJF) policy, with emphasis on non-preemption and the use of burst-time estimates to guide choices. In practice, estimates of CPU burst times may be derived from historical execution data or statistical prediction methods, such as exponential averaging. Because the algorithm prioritizes short jobs, longer processes may experience starvation if a continuous stream of short tasks arrives, especially in systems with dynamic arrival of processes.

Implementation considerations include the need for accurate burst-time estimation and the trade-off between optimal waiting times and fairness. SJN is primarily discussed in operating systems theory and education as a useful reference point for studying scheduling tradeoffs. Its practical applicability is limited in general-purpose, time-sharing systems where arrival times are unpredictable and burst estimates are unreliable.

In other domains, the acronym SJN may refer to different concepts or organizations; this article focuses on the computer science usage as Shortest Job Next.