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    Virtual Memory in Operating System.

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    hk1742010

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    Virtual Memory in Operating System.

    Uploaded by

    hk1742010
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    Virtual Memory in operating system.

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    13 views21 pages

    Virtual Memory in Operating System.

    Uploaded by

    hk1742010

    Copyright:

    © All Rights Reserved
    Download as PPTX, PDF, TXT or read online from Scribd
    Download as pptx, pdf, or txt
    of 21

    VIRTUAL MEMORY IN OS

    PRESENTED BY: SOMAN AHMAD


    ABDUL AZIZ
    DIGITAL COMMUNICATIONS

    WHAT IS VIRTUAL MEMORY?

    WHY NEED VIRTUAL MEMORY?

    HOW VIRTUAL MEMORY WORKS?

    ADVATAGES/DISADVANTAGES OF VIRTUAL MEMORY?

    WHAT IS DEMAND PAGING IN OS?

    BENEFITS OF DEMAND PAGING?


    VIRTUAL MEMORY

    INTRODUCTION

    Definition
     Virtual memory is a crucial memory management
    strategy providing an abstract layer over physical
    storage, allowing programs to act as if they have
    contiguous working memory.

    Function
     It allows a computer to compensate for physical
    memory shortages by temporarily transferring data
    between RAM and disk storage.
    WHY WE NEED VIRTUAL MEMORY?

    1. Running Larger Programs


     Virtual memory allows running larger programs than
    the available physical RAM.
    Example: Running resource-intensive applications that
    exceed the constraints of physical memory.

    2. Improving Performance
     Improve computer performance by making more
    efficient use of physical RAM.
    Example: By paging pages to and from the disk, the
    operating system optimizes the use of RAM, keeping
    frequently used pages in memory.
    CONTINUE…

    3. Concurrent Program Execution


     Virtual memory enables the concurrent execution of
    multiple programs.
    Example: Suppose you have a computer with 4 GB of
    physical RAM.
     Program A: Requires 2 GB of RAM.
     Program B: Requires 1.5 GB of RAM.
     Program C: Requires 1 GB of RAM.
    With virtual memory, the operating system can use a
    combination of RAM and disk space to create the
    illusion that each program has its dedicated space in
    memory.
    CONTINUE…

    4. Flexible Memory Management


     Virtual memory provides a more flexible memory
    management scheme.
    Example: Consider a computer with 2 GB of RAM. If
    there are three programs each requiring 1 GB, virtual
    memory allows the OS to swap portions of these
    programs between RAM and disk, enabling all three
    programs to run concurrently.
    PHYSICAL VS VIRTUAL MEMORY

    Physical Memory Virtual Memory

    Physical memory is the actual, tangible memory Virtual memory is a memory management technique that
    hardware installed in a computer. extends the usable memory beyond the physical RAM
    installed in the system.

    It serves as the immediate workspace for the CPU, It creates an illusion of a larger memory space by using a
    storing actively used data and programs combination of RAM and space on the hard disk.

    Access to data in physical memory is fast, making it When physical memory is insufficient to hold all the data
    crucial for quick retrieval and execution of instructions and programs actively in use, the operating system swaps
    by the CPU. portions of data between the RAM and the disk.
    HOW VIRTUAL MEMORY WORKS?

    Address Translation
     When a program is executed, it generates memory
    addresses to access data and instructions.
     These addresses are initially virtual addresses,
    meaning they refer to locations in virtual memory.

    Mapping to Physical Memory:


     The Memory Management Unit (MMU), a hardware
    component, translates virtual addresses to physical
    addresses.
     The MMU uses data structures, such as page tables,
    to map virtual addresses to corresponding physical
    addresses in RAM.
    HOW VIRTUAL MEMORY WORKS?

    Page Tables
     Virtual memory is often organized into fixed-size
    blocks called pages.
     The page table is a data structure that maintains the
    mapping between virtual pages and physical pages in
    RAM.
     Each entry in the page table contains information
    about the corresponding page's location in physical
    memory.

    Page Faults
     If a program tries to access data that is not currently
    in RAM (a page fault), it triggers the operating
    system to intervene.
    HOW VIRTUAL MEMORY WORKS?

    Swapping to Disk
     The operating system decides which pages to keep in
    RAM and which to move to disk based on factors
    like usage patterns.
     If a page is not in RAM, it is swapped from the disk
    into an available location in RAM.

    Demand Paging
     Virtual memory systems often use a strategy called
    demand paging, where pages are loaded into RAM
    only when they are needed, not preemptively.
    DIAGRAMMATICAL WORKING
    ADVANTAGES OF VIRTUAL MEMORY

    Concurrency Data Sharing


     Enables the concurrent execution of multiple  Common data can be shared between RAM and
    applications or programs. virtual memory.

    Dynamic Size Improved CPU Utilization


     Users can adjust the size of virtual memory,  Enhances CPU utilization by accommodating more
    providing flexibility. processes in main memory.

    Large Program Execution Cost Savings


     Allows running programs larger than the available  Saves costs by avoiding the need to purchase
    main memory. additional physical RAM.
    DISADVANTAGES OF VIRTUAL MEMORY

    Performance Impact: Overall System Performance:


     Slows down the computer as hard drive speed is  May impact the overall performance of the system
    slower than RAM. negatively.

    Application Switching Delay:


     Switching between applications takes more time due
    to swapping.

    Hard Drive Space Usage:


     Allocates space on the hard drive, reducing available
    user space.
    DEMAND PAGING

    Definition
     Demand paging is a strategy where the OS loads
    pages into RAM only when they are needed,
    reducing unnecessary initial loading.

    Advantage
     This minimizes the system's resource usage and
    speeds up the overall responsiveness of the operating
    system.

    Example
     Loading specific portions of a large application into
    RAM based on user interactions.
    HOW DEMAND PAGING WORKS?

    1. Page Fault Handling


     A page fault is generated when a process attempts to
    access a memory address or a page that isn’t
    currently available on the main memory.

    2. Page Replacement
     If the system doesn’t have enough free memory to
    load the requested page, it must select a page to evict
    from memory to make room for the requested page.
     The system uses a page replacement algorithm in
    order to select the page to evict.
    CONTINUE…
    Page Table Management
     The next step is to manage the page table. The
    operating system must maintain a page table for each
    process, which maps virtual pages to physical pages.
     The operating system must update the page table
    whenever a page is loaded or evicted from memory.

    Swapping
     When the operating system evicts a page from
    memory, it’s typically swapped to disk to make room
    for other pages.
     Additionally, the operating system must manage the
    swapping of pages between memory and disk.
    CONTINUE…

    Demand Paging Algorithms


     Demand paging requires complex algorithms and
    data structures to manage memory efficiently and
    ensure that processes have the memory resources
    they need to execute.
    ADVANTAGES OF DEMAND PAGING

    On-Demand Loading Cost Efficiency


     Loads only the pages demanded by the executing  Helps reduce the bill of material (BOM) cost,
    process, conserving memory resources. especially in devices like smartphones where main
    memory is expensive compared to secondary storage.
    Increased Process Concurrent Execution:  Enables cost savings in hardware resources.
     More processes can be loaded into main memory
    simultaneously, reducing context switching time.

    Reduced Loading Latency


     Decreases loading latency during program startup as
    less information is accessed from secondary storage.
    DISADVANTAGES OF DEMAND PAGING

    Initial Program Delay Security Risks


     Initial access to pages not in memory may cause  Potential security risks, including vulnerability to
    delays. timing attacks.
     Requires careful consideration of security
    Low-Cost Embedded Systems implications, especially in sensitive applications.
     Low-cost, low-power embedded systems may lack a
    memory management unit supporting page
    replacement. Thrashing
     There is a risk of thrashing, where repeated page
    Complexity in Memory Management
    faults occur excessively, impacting overall system
     Memory management, particularly with page
    performance.
    replacement algorithms, becomes more complex.

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