CPU Scheduling Algorithms in Operating Systems

CPU Scheduling Algorithms in Operating Systems

When it comes to managing and allocating processing power within an operating system, CPU scheduling is essential. It involves selecting processes from the ready queue and assigning them to available CPUs. Here's a look at some of the most common CPU scheduling algorithms used in operating systems:

First-Come, First-Served (FCFS)

The FCFS algorithm is one of the simplest CPU scheduling algorithms. In this method, the process that arrives first gets scheduled first, followed by the next process, and so on. For example, if we have three processes A, B, and C arriving at time t=0, t=2, and t=6 respectively, they will be scheduled in the order of FCFS - A, B, and C.

Shortest Job First (SJF)

Shortest Job First, also known as the Shortest Job Next algorithm, prioritizes the execution of jobs based on their expected duration. This means that the shortest job in the waiting line will be executed first. For instance, if we have two jobs, one with a duration of 5 units and another with a duration of 8 units, the shorter job of 5 units will be scheduled first.

Shortest Remaining Time First (SRTF)

Shortest Remaining Time First is similar to SJF except that it only schedules a process when its turn comes up, even if there are other smaller jobs ahead. To implement SRTF, you need to sort the list of jobs by their remaining time after every completion of a process. If a new process enters the system, it goes to the end of the sorted list.

Priority Scheduling

Priority scheduling is a complex algorithm where each process has an associated priority level. When multiple processes are ready to run, the one with the highest priority is selected. There are different ways to determine priorities such as priority being proportional to the size of the job, priority being constant, or priority changing dynamically as a function of the CPU usage. However, dynamic priority changes can lead to starvation, which is why static priority schemes are more commonly implemented.