Virtual Memory In Operating System

Virtual Memory in Operating systems is a memory management technique that creates an illusion of large, continuous memory space for processes by using both RAM and disk storage.

It enables an operating system to run large applications or multiple programs simultaneously, even if the available RAM is insufficient. In this blog, we will learn about virtual memory in operating system.

What is Virtual Memory In Operating System?

Virtual memory in operating system is a memory management capability of an operating system that uses hardware and software to allow a computer to compensate for physical memory shortages by temporarily transferring data from Random Access Memory (RAM) to disk storage.

Virtual address space is increased using active memory in RAM and inactive memory in Hard Disk Drives (HDDs) to form contiguous addresses that hold both the applications and their data. A system using virtual memory can load larger programs or multiple programs running at the same time, allowing each one to operate as if it has infinite memory without having to purchase more RAM.

Virtual memory is a facility that allows the program to address memory from a local point of view, without regard to the amount of main memory. Virtual memory is used to give programmers the illusion that they have a very large memory at their disposal, even though the computer actually has a relatively small main memory.

A virtual memory system provides a mechanism for translating program-generated addresses into the correct main memory location dynamically while programs are being executed in the CPU.

Virtual Memory: Major Takeaways

Virtual memory creates an illusion of a large, continuous memory space by using both RAM and disk storage.
It allows an operating system to run large applications or multiple programs even with limited RAM
The system temporarily moves inactive data from RAM to disk storage to compensate for memory shortages.
Virtual address space combines active memory in RAM and inactive memory on HDDs to create contiguous memory addresses.
It enables programs to operate as if they have infinite memory, reducing the need for extra RAM
Virtual memory helps programmers work with larger memory spaces than are physically available.
It dynamically translates addresses to correct memory locations during program execution.

How Does Virtual Memory Work?

Virtual memory operates by allowing the operating system to handle memory dynamically, swapping data between RAM and disk storage as needed. Let us go through a step-by-step breakdown of how it functions:

1. Memory Addressing and Mapping

Every process is given a virtual address space that is independent of the physical memory available. The operating system maintains a page table to map these virtual addresses to actual physical memory locations.

2. Loading Data into RAM (Demand Paging)

Instead of loading an entire program into RAM, the Operating system loads only the required portions (pages). The rest of the program remains on disk until needed. When a required page is not in RAM, the OS triggers a page fault and retrieves it from disk storage.

3. Swapping Pages (Page Replacement)

Since RAM has limited capacity, some pages must be removed to make space for new ones. The operating system uses page replacement algorithms to determine which page to swap out. The removed pages are stored back in swap space, making them available for later retrieval.

4. Managing Thrashing

If too many pages are being swapped in and out of memory rapidly, it leads to thrashing. The OS optimizes performance by adjusting working set sizes and limiting excessive page faults.

5. Process Execution and Multitasking

Virtual memory allows multiple processes to execute simultaneously without requiring all data to be in RAM at once. This enables efficient multitasking and memory sharing between applications.

Major Components of Virtual Memory

The major components of virtual memory include paging, segmentation, and page replacement algorithms. Let us discuss them in a bit of detail:

1. Paging

Paging is the most common virtual memory implementation. In this method, the OS divides memory into fixed-sized blocks called pages. Correspondingly, the disk storage is divided into page frames. When a program needs a page not in RAM. The page table maintains the mapping between virtual addresses and physical addresses.

2. Segmentation

Segmentation divides memory into logical segments such as functions, arrays, and global variables, instead of fixed-sized pages. Each segment has a unique segment number and offset. This method is more flexible but can lead to fragmentation issues.

3. Page Replacement Algorithms

Since RAM has limited space, the operating system must decide which pages to swap out when new pages are needed. Common page replacement algorithms include FIFO (First-In-First-Out), LRU (Least Recently Used), and Optimal Page Replacement.

What is Demand Paging in Virtual Memory?

The process of loading a page into memory on demand (whenever a page fault occurs) is known as demand paging. The process includes the following steps:

If the CPU tries to refer to a page that is currently not available in the main memory, it generates an interrupt indicating a memory access fault.
The OS puts the interrupted process in a blocking state. For the execution to proceed, the OS must bring the required page into the memory.
The OS will search for the required page in the logical address space.
The required page will be brought from logical address space to physical address space. The page replacement algorithms are used for the decision-making of replacing the page in physical address space.
The page table will be updated accordingly, and the signal will be sent to the CPU to continue the program execution, and it will place the process back into a ready state.

What is Thrashing in Virtual Memory?

Thrashing occurs when a system spends more time processing page faults rather than executing transactions. While processing page faults, it is necessary to appreciate the benefits of virtual memory, thrashing has a negative effect on the system. As the page fault rate increases, more transactions need processing from the paging device. The queue at the paging device increases, resulting in increased service time for a page fault.

While the transactions in the system are waiting for the paging device, CPU utilization, system throughput and system response time decrease, resulting in below-optimal performance of a system. Thrashing becomes a greater threat as the degree of multiprogramming of the system increases. Therefore, to increase CPU utilization, multiprogramming should be reduced.

Advantages of Virtual Memory In Operating System

Some of the major advantages of Virtual memory includes:

Run Larger Applications: Programs can be larger than available RAM, enabling high-end software execution.
Improved Multitasking: Multiple applications can run smoothly without interfering with each other.
Process Isolation: Ensures each process has its own memory space, preventing unauthorized access.
Efficient Memory Utilization: Only required data is kept in RAM, optimizing system resources
Cost-Effective: Eliminates the immediate need for expensive RAM upgrades

Disadvantages of Virtual Memory In Operating System

Some of the major disadvantages of virtual memory include

Slower Performance: Disk access is much slower than RAM, leading to potential bottlenecks
Thrashing: Excessive page swapping can degrade system performance, making it less responsive
Complex Implementation: Requires additional OS overhead to manage memory efficiently
Higher Disk Wear and Tear: Frequent disk usage can reduce the lifespan of storage devices, especially HDDs

Become an Expert In DevOps with PW Skills

Discover a wide range of career opportunities in DevOps and Cloud Computing with the PW Skills DevOps and Cloud Computing Course and master in-demand tools like Ansible, Kubernetes, Jenkins, and more with our interactive coursework, dedicated mentors and more. Get real-world projects, practice exercises, module assignments to help you strengthen everything you learnt throughout the course.

Hurry! Enroll in this course and start your learning journey. Become a certified devOps engineer with pwskills.com.

Virtual Memory in Operating System FAQs

Q1. What is Virtual Memory in operating system?

Ans. Virtual memory is a memory management capability of an operating system that uses hardware and software to allow a computer to compensate for physical memory shortages by temporarily transferring data from Random Access Memory (RAM) to disk storage.

Q2. What is Demand Paging?

Ans. The process of loading a page into memory on demand (whenever a page fault occurs) is known as demand paging.

Q3. What is Thrashing?

Ans. Thrashing occurs when a system spends more time processing page faults rather than executing transactions. While processing page faults, it is necessary to appreciate the benefits of virtual memory, thrashing has a negative effect on the system.

Q4. What is Paging?

Ans. Paging is the most common virtual memory implementation. In this method, the OS divides memory into fixed-sized blocks called pages. Correspondingly, the disk storage is divided into page frames.