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

Semaphore in Operating System

What is Semaphore in Operating System

Semaphore is defined as an integer variable which is used to solve the problem of the critical section in process synchronization. In semaphore, we use two types of atomic operations, and that operations are wait and signal.

The definitions of wait and signal are as follows:

Wait: - In wait operation, the argument ‘S’ value is decrement by 1 if the value of the ‘S’ variable is positive. If the value of the argument variable ‘S’ is zero or negative, no operation is performed.

Semaphore in Operating System

Signal: - In Signal atomic operation, the value of the argument variable ‘S’ is incremented.

Semaphore in Operating System

Characteristic of Semaphore

There are following characteristics of Semaphore:

  1. Semaphore carries a non-negative integer value always.
  2. We use semaphore mechanism to offer synchronization of tasks.
  3. It is a low-level synchronization mechanism.

Types of Semaphores

We have following two types of Semaphores:

  1. Counting Semaphores
  2. Binary Semaphores
  1. Counting Semaphores: - Counting Semaphore is defined as a semaphore that contains integer values, and these values have an unrestricted value domain. A counting semaphore is helpful to coordinate the resource access, which includes multiple instances.
  2. Binary Semaphores: - Binary Semaphores are also called Mutex lock. There are two values of binary semaphores, which are 0 and 1. The value of binary semaphore is initialized to 1. We use binary semaphore to remove the problem of the critical section with numerous processes.

Advantages of Semaphore

There are following advantages of semaphore:

  1. In the Semaphore, only one process is allowed to enter into the critical section. In this, the principle of mutual exclusion is to be followed strictly. And the semaphore mechanism is a more efficient mechanism than other methods which we use in process synchronization.
  2. It is machine-independent because it is implemented in the microkernel’s machine-independent code.
  3. With the help of the semaphore, the resources are managed flexibly.
  4. In semaphore, there is a busy waiting, so there is no wastage of resources and process time.
  5. In the semaphore, more threads are permitted to enter into the critical section.

Disadvantages of Semaphore

There are following disadvantages of Semaphore:

  1. There is a priority inversion in the semaphore, and this is the biggest drawback of the semaphore.
  2. In the semaphore, due to program error violation of mutual exclusion, deadlock can be happened.
  3. In the semaphore, there are more chances of programmer errors.
  4. For the purpose of large-scale use, the semaphore is not a practical method, and due to this, there may be loss of modularity.
  5. The Programming of the semaphore is tough, so there may be a possibility of not achieving mutual exclusion.
  6. In the semaphore, the OS has to preserve all calls to wait and signal semaphore.

Difference between Counting Semaphore and Binary Semaphore

Counting SemaphoreBinary Semaphore
In counting semaphore, there is no mutual exclusion.In binary semaphore, there is mutual exclusion.
In the counting semaphore, any integer value can be possible.It contains only two integer values that are 1 and 0.
In counting semaphore, there are more than one slots.In the binary semaphore, there is only one slot.
The counting process offers a set of processes.Binary semaphore contains mutual exclusion mechanism.

Difference between Semaphore and Mutex

 Parameter Semaphore Mutex
Data TypeIt is an integer variable.It is an object.
MechanismSemaphore is a signaling mechanism.Mutex is a type of locking mechanism.
TypesThere are two types of semaphore, which are binary semaphore and counting semaphore.There are no types of mutex.
OperationIn semaphore, wait() and signal() operations are performed to modify the value of semaphore.In mutex, locked or unlocked operation is performed.
ThreadIn semaphore, there may be multiple program threads.In mutex, there may also be a multiple program thread but not simultaneously.