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What Are The Four Types Of Scheduling

Scheduling is an important part of any project or task. It involves organizing resources, time, and other activities that are needed to complete a project.

Different types of scheduling algorithms can be used to make allocating resources or managing activities easier. In this article, we will discuss the four types of scheduling with an in-depth analysis to understand project and task management better.

1. Non-Preemptive Scheduling

Non-preemptive Scheduling is a type of scheduling where once a process starts, it runs until its completion. In this type of scheduling, the resources are allocated to the running process until it finishes its execution. If a new process arrives, it is not allowed to proceed until the running process has completed.

Examples of non-preemptive scheduling include first-come-first-served, priority scheduling, and round-robin. The first-come-first-served (FCFS) scheduling algorithm is based on the concept of giving priority to processes that arrive first in the system.

In this method, the process that arrives first is given the highest priority and is executed first. This process is then followed by the process that arrived second and so on.

The advantage of this scheduling algorithm is that it is easy to implement. The priority scheduling algorithm is based on assigning a priority to each process based on some measure such as CPU burst time, memory requirements, or I/O operations. Processes with higher priority are allocated the CPU first and process with low priority are allocated to the CPU last.

One drawback of this scheduling algorithm is that it may cause starvation of low priority processes. Finally, the round-robin scheduling algorithm assigns equal time slices to all the processes in the queue. Each process is allowed to use the CPU for the time slice it is given and then is moved back to the end of the queue.

The advantage of this algorithm is that it prevents starvation of processes.

2. Preemptive Scheduling

Preemptive Scheduling is a process by which the running process can be interrupted and put on hold so that a new process can be started. In this type of scheduling, the operating system interrupts the running process in order to allocate resources for the new process. Examples of Preemptive Scheduling algorithms include earliest-deadline-first, shortest-remaining-time-first and Multi-Level Queue Scheduling.

The earliest-deadline-first (EDF) scheduling algorithm allocates the CPU to the process that has the earliest deadline. In other words, the process with the smallest amount of time left before its completion is given the highest priority.

This algorithm prevents processes from missing their deadlines and can be beneficial in real-time systems. The shortest-remaining-time-first (SRTF) scheduling algorithm assigns the CPU to the process with the shortest remaining time on the CPU.

This ensures processes with a higher priority are completed faster while also allowing processes with lower priority to run, preventing starvation. Multi-level queue scheduling is a Preemptive Scheduling algorithm that assigns processes to multiple queues according to their priority. When a new process arrives in the system, the operating system checks the queue level assigned to the process and executes the existing process of the same level first.

The advantage of this algorithm is that it is easy to implement and efficient in managing processes with different priorities.

3. Real-Time Scheduling

Real-time scheduling is a type of scheduling in which the completion time of a process has to be met without fail. This type of scheduling requires very quick response times, usually within a few milliseconds.

Examples of Real-time scheduling algorithms include Rate Monotonic Scheduling, Earliest Deadline First and Least Laxity First. Rate Monotonic Scheduling (RMS) is the most commonly used Real-time scheduling algorithm. It assigns a static priority to each process and arranges them in the order of their static priorities.

This ensures that the process with the highest priority is always executed first. Earliest Deadline First (EDF) scheduling algorithm executes the process with the earliest deadline. It is similar to the standard Preemptive Scheduling algorithms but with one major difference; the deadline of a process has to be met without fail.

Least Laxity First (LLF) is a scheduling algorithm that takes into consideration the amount of time a process has remaining until its completion. Higher priority is given to the process that has the least amount of time remaining and all other processes are delayed until this process is completed.

4. Advanced Scheduling

Advanced scheduling is a type of scheduling algorithm designed to handle complex tasks. It is based on two principles; one is to break down the task into smaller pieces and the other is to plan for possible contingencies. Examples of advanced scheduling algorithms include Dynamic Resource Allocation (DRA), Packing Algorithm (PA) and Maximum Contingency Scheduling.

Dynamic Resource Allocation (DRA) scheduling algorithms allocate resources to the process only when needed. This helps reduce the system cost and improves the overall execution time of the process.

The Packing Algorithm (PA) is another advanced scheduling algorithm used to minimize the system cost in situations where multiple processes compete for resources. Its goal is to find the best combination of tasks in order to minimize resource wastage while maximizing the system performance. Maximum Contingency Scheduling is used in emergency situation where there is a tight deadline but room for possible contingencies.

It assigns tasks to the resources regardless of any uncertainties and adjusts them in case of any emergency situation.


Scheduling is an important part of project and task management. Different types of scheduling algorithms can be used to allocate resources and manage processes efficiently.

This article discussed the four types of scheduling algorithms; Non-preemptive scheduling, Preemptive scheduling, Real-time scheduling, and Advanced scheduling. Each type of scheduling algorithm has its own advantages and disadvantages which makes it important to choose the algorithm carefully according to the project or task.

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