Scheduling algorithms play a crucial role in operating systems and determine the order in which processes or tasks are executed on a computer system. Similar to humans, computers also have the need to fix a certain schedule to perform their tasks. These algorithms are responsible for managing the allocation of system resources and ensuring efficient utilization of the CPU. Scheduling algorithms can be broadly categorized into different types based on their characteristics and scheduling strategies. Additionally, these algorithms can be further classified as preemptive or non-preemptive, depending on whether a running process can be interrupted or not. Let’s explore these concepts further:
1. First-Come, First-Served (FCFS):
First-Come, First-Served (FCFS) is a non-preemptive scheduling algorithm where processes are executed in the order they arrive. The first process to arrive is the first to be executed. However, FCFS may suffer from the “convoy effect” when a long-running process delays subsequent processes, resulting in poor overall performance. This algorithm is simple to understand and implement but may not be suitable for time-sensitive or interactive applications.
2. Shortest Job Next (SJN) or Shortest Job First (SJF):
Shortest Job Next (SJN), also known as Shortest Job First (SJF), is a non-preemptive scheduling algorithm that selects the process with the smallest total execution time next. It prioritizes shorter jobs, aiming to minimize average waiting time. SJN requires knowing the execution time of each process in advance, which is often difficult to estimate accurately. It can lead to starvation if a long job constantly arrives, preventing shorter jobs from executing.
3. Round Robin (RR):
Round Robin (RR) is a preemptive scheduling algorithm where each process is assigned a fixed time slice or quantum to execute. If a process does not complete within its time slice, it is preempted, and the next process in the queue is scheduled. RR ensures fairness by allowing each process to get a chance to execute but can suffer from high context-switching overhead. It is suitable for time-sharing systems and provides good response time.
4. Priority Scheduling:
Priority Scheduling assigns a priority value to each process, and the process with the highest priority executes first. It can be either preemptive (preemptive priority scheduling) or non-preemptive (non-preemptive priority scheduling). Preemptive priority scheduling allows a higher-priority process to interrupt a lower-priority process during execution, while non-preemptive priority scheduling allows a process to complete its execution before selecting the next process. Priority scheduling ensures that higher-priority processes get preferential treatment but can lead to starvation if lower-priority processes are constantly delayed.
5. Shortest Remaining Time (SRT):
Shortest Remaining Time (SRT) is a preemptive version of the SJN algorithm. It selects the process with the shortest remaining execution time to execute next. If a new process arrives with a shorter remaining time than the currently running process, it preempts the current process. SRT provides optimal average waiting time but requires accurate estimations of execution time, which can be challenging in practice.
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6. Multilevel Queue Scheduling:
Multilevel Queue Scheduling categorizes processes into multiple priority queues. Each queue has its scheduling algorithm and priority level. Processes are initially placed in the highest priority queue and move to lower priority queues as they consume their allotted time or are based on specific criteria. Preemptive or non-preemptive algorithms can be used within each queue. Multilevel queue scheduling provides a way to differentiate processes based on priority or type, allowing for efficient management of various types of workloads.
7. Multilevel Feedback Queue Scheduling:
Multilevel Feedback Queue Scheduling is an extension of multilevel queue scheduling. It allows processes to move between different queues based on their behavior. A process that uses excessive CPU time may be moved
With that, we have various types of scheduling algorithms that are useful in a computer system daily. Now one may think as to why and how does this necessary help? This was more of an educational topic to help understand the concept of scheduling algorithms in a more detailed and great way. We always used to think about how our computers were able to multitask and have all these tasks working at the same time. Well now, that has been debunked and understood as to how each algorithm works and how it transitions between each task within fractions of seconds to provide us with the easiest and fastest way to perform a task.
Operating System is a really fun topic to learn about as it ventures into detail as to how our PC works, functions, troubleshoots, and how it performs these tasks with those fraction of seconds of intervals. Hope this article helped you understand it a tad bit better and was informational about the working of the operating system.