Comparison of Different CPU Scheduling Algorithms in OS
Last Updated :
30 Nov, 2021
A scheduling algorithm is used to estimate the CPU time required to allocate to the processes and threads. The prime goal of any CPU scheduling algorithm is to keep the CPU as busy as possible for improving CPU utilization.
Scheduling Algorithms
1. First Come First Serve(FCFS): As the name implies that the jobs are executed on a first come first serve basis. It is a simple algorithm based on FIFO that's first in first out. The process that comes first in the ready queue can access the CPU first. If the arrival time is less, then the process will get the CPU soon. It can suffer from the convoy effect if the burst time of the first process is the longest among all the jobs.
2. Shortest Job First (SJF): Also known as the shortest job first or shortest job next is a non-preemptive type algorithm that is easy to implement in batch systems and is best in minimizing the waiting time. It follows the strategies where the process that is having the lowest execution time is chosen for the next execution.
3. Longest Job First Scheduling(LJF): The longest job first (LJF) is the non-preemptive version. This algorithm is also based upon the burst time of the processes. The processes are put into the ready queue according to their burst times and the process with the largest burst time is processed first.
4. Longest Remaining Time First Scheduling (LRTF): The preemptive version of LJF is LRTF. Here the process with the maximum remaining CPU time will be considered first and then processed. And after some time interval, it will check if another process having more Burst Time arrived up to that time or not. If any other process has more remaining burst time, so the running process will get pre-empted by that process.
5. Shortest Remaining Time First(SRTF): This algorithm is based on SJF and this is the preemptive version of SJF. In this scheduling algorithm, the process with the smallest remaining burst time is executed first and it may be preempted with a new job that has arrived with a shorter execution time.
6. Round Robin(RR): It is a preemptive scheduling algorithm in which each process is given a fixed time called quantum to execute. At this time one process is allowed to execute for a quantum and then preempts and then another process is executed. In this way, there is context switching between processes to save states of these preempted processes.
7. Priority Scheduling: It is a non-preemptive algorithm that works in batch systems and, each process is assigned with a priority and the process with the highest priority is executed first. This can lead to starvation for other processes.
8. Multiple Levels Queues Scheduling: In this scheduling, multiple queues have their scheduling Algorithms and are maintained with the processes that possess the same characteristics. For this, priorities are assigned to each queue for the jobs to be executed.
9. Multilevel-Feedback-Queue Scheduler: It defines several queues and the scheduling algorithms for each queue. This algorithm is used to determine when to upgrade a process when to demote a process, and also determine the queue in which a process will enter and when that process needs service.
Note: The SJF scheduling algorithm is hypothetical and un-implementable, as it is impossible to determine the burst time of any process without running it. SJF is a benchmarking algorithm as it provides minimum waiting time than any other scheduling algorithm
Comparative Analysis of Different CPU Scheduling Algorithms
Here is a brief comparison between different CPU scheduling algorithms:
| Algorithm | Allocation is | Complexity | Average waiting time (AWT) | Preemption | Starvation | Performance |
|---|
| FCFS | According to the arrival time of the processes, the CPU is allocated. | Not complex | Large. | No | No | Slow performance |
|---|
| SJF | Based on the lowest CPU burst time (BT). | More complex than FCFS | Smaller than FCFS | No | Yes | Minimum Average Waiting Time |
|---|
| LJFS | Based on the highest CPU burst time (BT) | More complex than FCFS | Depending on some measures e.g., arrival time, process size, etc. | No | Yes | Big turn-around time |
|---|
| LRTF | Same as LJFS the allocation of the CPU is based on the highest CPU burst time (BT). But it is preemptive | More complex than FCFS | Depending on some measures e.g., arrival time, process size, etc. | Yes | Yes | The preference is given to the longer jobs |
|---|
| SRTF | Same as SJF the allocation of the CPU is based on the lowest CPU burst time (BT). But it is preemptive. | More complex than FCFS | Depending on some measures e.g., arrival time, process size, etc | Yes | Yes | The preference is given to the short jobs |
|---|
| RR | According to the order of the process arrives with fixed time quantum (TQ) | The complexity depends on TQ size | Large as compared to SJF and Priority scheduling. | No | No | Each process has given a fairly fixed time |
|---|
| Priority Pre-emptive | According to the priority. The bigger priority task executes first | This type is less complex | Smaller than FCFS | Yes | Yes | Well performance but contain a starvation problem |
|---|
| Priority non-preemptive | According to the priority. with monitoring the new incoming higher priority jobs | This type is less complex than Priority preemptive | preemptive Smaller than FCFS | No | Yes | Most beneficial with batch systems |
|---|
| MLQ | According to the process that resides in the bigger queue priority | More complex than the priority scheduling algorithms | Smaller than FCFS | No | Yes | Good performance but contain a starvation problem |
|---|
| MFLQ | According to the process of a bigger priority queue. | It is the most Complex but its complexity rate depends on the TQ size | Smaller than all scheduling types in many cases | No | No | Good performance |
|---|
Similar Reads
Operating System Tutorial
An Operating System(OS) is a software that manages and handles hardware and software resources of a computing device. Responsible for managing and controlling all the activities and sharing of computer resources among different running applications.A low-level Software that includes all the basic fu
4 min read
Types of Operating Systems
Operating Systems can be categorized according to different criteria like whether an operating system is for mobile devices (examples Android and iOS) or desktop (examples Windows and Linux). Here, we are going to classify based on functionalities an operating system provides. 8 Main Operating Syste
11 min read
ASCII Values Alphabets ( A-Z, a-z & Special Character Table )
ASCII (American Standard Code for Information Interchange) is a standard character encoding used in telecommunication. The ASCII pronounced 'ask-ee', is strictly a seven-bit code based on the English alphabet. ASCII codes are used to represent alphanumeric data. The code was first published as a sta
7 min read
CPU Scheduling in Operating Systems
CPU scheduling is a process used by the operating system to decide which task or process gets to use the CPU at a particular time. This is important because a CPU can only handle one task at a time, but there are usually many tasks that need to be processed. The following are different purposes of a
8 min read
Page Replacement Algorithms in Operating Systems
In an operating system that uses paging for memory management, a page replacement algorithm is needed to decide which page needs to be replaced when a new page comes in. Page replacement becomes necessary when a page fault occurs and no free page frames are in memory. in this article, we will discus
6 min read
Difference Between IPv4 and IPv6
In the digital world, where billions of devices connect and communicate, Internet Protocol (IP) Addresses play a crucial role. These addresses are what allow devices to identify and locate each other on a network. To know all about IP Addresses - refer to What is an IP Address? Currently, there are
9 min read
Difference between BFS and DFS
Breadth-First Search (BFS) and Depth-First Search (DFS) are two fundamental algorithms used for traversing or searching graphs and trees. This article covers the basic difference between Breadth-First Search and Depth-First Search. ParametersBFSDFSStands forBFS stands for Breadth First Search.DFS st
2 min read
Introduction of Deadlock in Operating System
A deadlock is a situation where a set of processes is blocked because each process is holding a resource and waiting for another resource acquired by some other process. In this article, we will discuss deadlock, its necessary conditions, etc. in detail. Deadlock is a situation in computing where tw
11 min read
Disk Scheduling Algorithms
Disk scheduling algorithms are crucial in managing how data is read from and written to a computer's hard disk. These algorithms help determine the order in which disk read and write requests are processed, significantly impacting the speed and efficiency of data access. Common disk scheduling metho
12 min read
What is a Neural Network?
Neural networks are machine learning models that mimic the complex functions of the human brain. These models consist of interconnected nodes or neurons that process data, learn patterns, and enable tasks such as pattern recognition and decision-making. In this article, we will explore the fundament
14 min read