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

What is Page Replacement in Operating System?

Page replacement is a crucial concept in operating systems that involves swapping out pages of data from a computer's RAM to a storage device, such as a hard drive, when the system needs to allocate more space for running processes. The goal of page replacement is to optimize the use of available memory by swapping out the least frequently accessed pages, and thereby ensuring that frequently accessed pages remain in RAM for faster access.   

What is Page Replacement?

The concept of page replacement is based on the virtual memory system, which is a technique used by modern operating systems to simulate more memory than is physically available. The virtual memory system divides the available physical memory into equal-sized chunks, called pages, and maps these pages to corresponding pages on the storage device.

When a program needs to access a page that is not currently in RAM, the system generates a page fault, which triggers a process called page replacement. The page replacement algorithm selects a page to remove from RAM, making space for the new page to be loaded. The removed page is then written to the storage device.

Different Page Replacement Algorithms

There are several different page replacement algorithms that can be used to decide which page to remove from RAM. These include the following:

First-In, First-Out (FIFO)

The FIFO algorithm removes the oldest page in memory. In this approach, the first page that was loaded into memory is the first page that is removed. FIFO is a simple algorithm but may not be the most efficient, as it may remove a frequently accessed page.

Least Recently Used (LRU)

The LRU algorithm removes the least recently used page in memory. This algorithm is based on the assumption that pages that have not been accessed recently are less likely to be needed in the near future. LRU is generally considered to be a more efficient algorithm than FIFO, as it tends to remove less frequently accessed pages.

Optimal Page Replacement (OPT)

The OPT algorithm is a theoretical algorithm that selects the page that will not be used for the longest period of time in the future. While OPT is the most efficient page replacement algorithm in theory, it is not practical to implement in real-time systems, as it requires knowledge of future page accesses.

Clock Algorithm

The clock algorithm, also known as the second chance algorithm, is a variation of the FIFO algorithm that considers the page's reference bit. When a page is referenced, its reference bit is set to 1. The clock algorithm maintains a circular list of pages and checks each page's reference bit. If the reference bit is 0, the page is removed, and if the reference bit is 1, it is given a second chance and its reference bit is set to 0.

Random Page Replacement

The random page replacement algorithm randomly selects a page from memory for replacement. This algorithm is simple to implement but may not be the most efficient, as it may remove frequently accessed pages.

Choosing the right page replacement algorithm

The choice of page replacement algorithm depends on the specific requirements of the system. For example, a system with a small amount of memory may benefit from an algorithm that removes less frequently accessed pages, such as LRU or the clock algorithm. A system with a large amount of memory may be able to use a simpler algorithm, such as FIFO or random page replacement.

One important consideration when choosing a page replacement algorithm is the system's workload. Different workloads may have different access patterns for memory pages, which can affect the efficiency of the algorithm. For example, a workload with many frequently accessed pages may benefit from an algorithm that prioritizes these pages, such as LRU. On the other hand, a workload with many randomly accessed pages may be better served by a simpler algorithm, such as FIFO or random page replacement.

Another consideration is the size of the system's memory. A system with a small amount of memory may need to be more selective in choosing which pages to keep in RAM, as there may be less space available. In this case, a more complex algorithm, such as LRU or the clock algorithm, may be more efficient. A system with a large amount of memory, on the other hand, may be able to use a simpler algorithm, as there is more space available to store pages in RAM.

It's worth noting that some modern operating systems use a combination of page replacement algorithms, rather than relying on a single algorithm. For example, the Windows operating system uses a hybrid approach that combines LRU with the clock algorithm. This approach allows the system to take advantage of the benefits of both algorithms and improve overall efficiency.

In addition to the choice of page replacement algorithm, there are several other factors that can affect the performance of the virtual memory system. These include the size of the page, the size of the page table, and the speed of the storage device. Choosing the optimal values for these parameters requires careful tuning and testing to ensure the best possible performance.


In conclusion, page replacement is a critical aspect of modern operating systems that allows them to efficiently manage memory usage. By choosing the right page replacement algorithm and carefully tuning system parameters, a system can improve its performance and reduce the likelihood of page faults. As the demand for memory-intensive applications continues to grow, the importance of page replacement will only continue to increase.