Operating System Tutorial

Operating System Tutorial Types of Operating System Evolution of Operating System Functions of Operating System Operating System Properties Operating System Services Components of Operating System Needs of the Operating System

Operating Systems

Linux Operating System Unix Operating System Ubuntu Operating System Chrome Operating Systems Fedora Operating System MAC Operating System MS Windows Operating System Solaris Operating System Cooperative Operating System CorelDRAW Operating System CentOS FreeBSD Operating Systems Batch Operating System MS-DOS Operating System Commercial Mobile Operating Systems


Difference Between Multi-programming and Multitasking Difference between C-LOOK and C-SCAN Difference between Rotational Latency and Disk Assess Time Trap vs Interrupt Difference between C-SCAN and SSTF Difference between SCAN and FCFS Difference between Seek Time and Disk Access Time Difference between SSTF and LOOK Difference between Process and Program in the Operating System Difference between Protection and Security in Operating System

How To

How to implement Monitors using Semaphores How to Install a Different Operating System on a PC


What is Kernel and Types of Kernel What is DOS Operating System What is Thread and Types of Thread What is Process Scheduler and Process Queue What is Context Switching What is CPU Scheduling What is Producer-Consumer Problem What is Semaphore in Operating System Monitors in Operating System What is Deadlock What is Paging and Segmentation What is Demand Paging What is Virtual Memory What is a Long term Scheduler What is Page Replacement in Operating System What is BSR Mode What is Convoy Effect What is Job Sequencing in Operating System Why is it critical for the Scheduler to distinguish between I/O-bound and CPU-bound programs Why is there a Need for an Operating System


Process Management Process State Scheduling Algorithm FCFS (First-come-First-Serve) Scheduling SJF (Shortest Job First) Scheduling Round-Robin CPU Scheduling Priority Based Scheduling HRRN (Highest Response Ratio Next) Scheduling Process Synchronization Lock Variable Mechanism TSL Mechanism Turn Variable Mechanism Interested Variable Mechanism Deadlock Avoidance Strategies for Handling Deadlock Deadlock Prevention Deadlock Detection and Recovery Resource Allocation Graph Banker’s Algorithm in Operating System Fixed Partitioning and Dynamic Partitioning Partitioning Algorithms Disk Scheduling Algorithms FCFS and SSTF Disk Scheduling Algorithm SCAN and C-SCAN Disk Scheduling Algorithm Look and C-Look Disk Scheduling Algorithm File in Operating System File Access Methods in Operating System File Allocation Method Directory Structure in Operating System N-Step-SCAN Disk Scheduling Feedback Queue in Operating System Contiguous Memory Allocation in Operating System Real-time Operating System Starvation in Operating System Thrashing in Operating System 5 Goals of Operating System Advantages of Operating System Advantages of UNIX Operating System Bit Vector in Operating System Booting Process in Operating System Can a Computer Run Without the Operating System Dining Philosophers Problem in Operating System Free Space Management in Operating System Inter Process Communication in Operating System Swapping in Operating System Memory Management in Operating System Multiprogramming Operating System Multitasking Operating Systems Multi-user Operating Systems Non-Contiguous Memory Allocation in Operating System Page Table in Operating System Process Scheduling in Operating System Segmentation in Operating System Simple Structure in Operating System Single-User Operating System Two Phase Locking Protocol Advantages and Disadvantages of Operating System Arithmetic operations in binary number system Assemblers in the operating system Bakery Algorithm in Operating System Benefits of Ubuntu Operating System CPU Scheduling Criteria in Operating System Critical Section in Operating System Device Management in Operating System Linux Scheduler in Operating System Long Term Scheduler in Operating System Mutex in Operating System Operating System Failure Peterson's Solution in Operating System Privileged and Non-Privileged Instructions in Operating System Swapping in Operating System Types of Operating System Zombie and Orphan Process in Operating System 62-bit operating system Advantages and Disadvantages of Batch Operating System Boot Block and Bad Block in Operating System Contiguous and Non - Contiguous Memory Allocation in Operating System Control and Distribution Systems in Operations Management Control Program in Operating System Convergent Technologies in Operating System Convoy Effect in Operating System Copy Operating Systems to SSD Core Components of Operating System Core of UNIX Operating System Correct Value to return to the Operating System Corrupted Operating System Cos is Smart Card Operating System Cosmos Operating Systems Examples Generation of Operating System Hardware Solution in Operating System Process Control Block in Operating System Function of Kernel in Operating System Operating System Layers History of Debian Operating Systems Branches and Architecture of Debian Operating Systems Features and Packages of Debian Operating Systems Installation of Operating System on a New PC Organizational Structure and Development in Debian Operating Systems User Interface in Operating System Types Of Memory in OS Operating System in Nokia Multilevel Paging in OS Memory Mapping Techniques in OS Memory Layout of a Process in Operating System Hardware Protection in Operating System Functions of File Management in Operating System Core of Linux Operating System Cache Replacement Policy in Operating System Cache Line and Cache Size in Operating System What is Memory Mapping? Difference Between Network Operating System And Distributed Operating System What is the difference between a Hard link and a Soft Link? Principles of Preemptive Scheduling Process Scheduling Algorithms What is NOS? What is the Interrupt I/O Process? What is Time Sharing OS What is process termination? What is Time-Sharing Operating System What is Batch File File system manipulation What is Message-passing Technique in OS Logical Clock in Distributed System

FCFS Scheduling in OS

FCFS: First Come First Serve Scheduling in OS

FCFS is a non-preemptive and preemptive scheduling algorithm that is easy to understand and use. In this, the process which reaches first is executed first, or in other words, the process which requests first for a CPU gets the CPU first.

Example of FCFS: buying tickets at the ticket counter.

FCFS is similar to the FIFO queue data structure. In FCFS, the element which is added in the queue first will leave first.

FCFS is used in Batch Operating Systems.

Characteristics of FCFS Scheduling

The characteristics of FCFS Scheduling are:

  1. FCFS is simple to use and implement.
  2. In FCFS, jobs are executed in a First-come First-serve (FCFS) manner.
  3. FCFS supports both preemptive as well as non-preemptive scheduling algorithm.
  4. FCFS is poor in performance due to high waiting times.

Advantages of FCFS

The advantages of FCFS are:

  1. Easy to program
  2. First come, first serve
  3. Simple scheduling algorithm.

Disadvantages of FCFS

  1. Because of non-preemptive nature, the problem of starvation arises.
  2. More Average waiting time.
  3. Due to its simplicity, FCFS is not effective.
  4. FCFS is not the ideal scheduling for the time-sharing system.
  5. FCFS is a Non-Preemptive Scheduling algorithm, so allocating the CPU to a process will never release the CPU until it completes its execution.
  6. In FCFS, it is not possible to use the resources in a parallel manner, which causes the convoy effect, so the resource utilization is poor in FCFS.

What is Convoy Effect

In FCFS, Convoy Effect is a condition that arises in the FCFS Scheduling algorithm when one process holds the CPU for a long time, and another process can get the CPU only when the process holding the CPU finishes its execution. Due to this, resource utilization is poor and also affects the performance of the operating system.

Example of FCFS Scheduling

In the following example, we have 4 processes with process ID P0, P1, P2, and P3. The arrival time of P0 is 0, P1 is 1, P2 is 2, and P3 is 3. The arrival time and burst time of the processes are given in the following table.

The waiting time and Turnaround time are calculated with the help of the following formula.

         Waiting Time = Turnaround time – Burst Time

          Turnaround Time = Completion time – Arrival time 

Process ID Arrival Time Burst Time Completion Time Turnaround Time Waiting Time
P0 0 6 6 6 0
P1 1 8 14 13 5
P2 2  10 24 22 12
P3 3 12 36 33 21
FCFS Scheduling in OS

Average Waiting Time = 0+5+12+21/4

                                         = 38/4

                                          = 9.5 ms

Average Turnaround Time = 6+13+22+33/4


                                               = 18.5 ms