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7_Physical Pages and Frames.md

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Physical Pages and Frames 📚 🧠

  • Physical Memory:

    • It refers to the Random Access Memory (RAM) in a computer system.

    • For example , the physical memory is 4GB, which means the address of the last byte in this memory will be (2^{32} - 1).

  • Frames:

    • Physical memory is logically divided into blocks of equal size known as frames.
    • A commonly chosen size for a frame is 4KB, though it can be configured differently.
    • Total frames in the given 4GB of physical memory can be calculated using (\text{Total Frames} = \frac{\text{Size of Physical Memory}}{\text{Size of one Frame}}), leading to (2^{20}) frames in a 4GB memory if using 4KB frames.

  • Physical Pages:

    • A physical page is essentially a snapshot of the data stored in a frame of physical memory.
    • The size of a physical page is equal to the size of a frame (in this case, 4KB).
    • If you visualize a frame (a block of physical memory) and take a “picture” or snapshot of the data within it, that snapshot is what’s referred to as a physical page.

  • Analogy for Understanding Pages and Frames:

    • A container that can carry three apples is analogous to a frame in physical memory which can contain a set amount of data.
    • Moving batches of apples with the container to transport a larger total amount (e.g., nine apples) is like moving physical pages (snapshots of data) in and out of the physical frames to utilize or manipulate more data than the frame can hold at one time.

Curiosity 🧐

  1. Q: What factors might influence the chosen size of a memory frame and why might 4KB be considered optimal in many cases? A: The size of a memory frame can be influenced by factors like page table size, disk I/O, and memory management overhead. 4KB is often chosen because it offers a balance, keeping the page table size manageable while also facilitating efficient disk I/O and minimizing the overhead associated with managing many small pages or the wastage associated with managing fewer, larger pages.

  2. Q: How does the operating system manage data transfer between physical pages in memory and those stored on a disk? A: The OS uses a Paging system, where it swaps data (pages) in and out of physical memory and disk storage as needed. It uses a Page Table to keep track of where each page of the virtual memory is stored, either in the physical memory or on the disk.

  3. Q: Explain the significance of having physical pages and frames in the memory management of an operating system? A: Physical pages and frames facilitate efficient management of memory, allowing the OS to manipulate and use more data than could fit into physical memory by utilizing disk storage as supplementary virtual memory. This mechanism enables multi-tasking and running large applications smoothly even with limited RAM.

  4. Q: Could you explain how memory fragmentation is affected by the concept of physical pages and frames? A: Physical pages and frames help to mitigate issues related to memory fragmentation. Since memory is divided into fixed-size blocks (frames), and data (pages) are swapped in and out of these blocks, it avoids the problem of having scattered, unusable memory spaces (fragmentation) that can occur with variable-sized allocation.

Concepts in Simple Words 🗣

Think of physical memory (RAM) like a big bookshelf 📚. Each shelf (frame) is designed to hold a specific size of books (data) neatly, which in our case is a 4KB size book. The entire bookshelf might have a huge capacity (like 4GB), but each shelf can only hold one book at a time.

Now, let's imagine you have many books (data) that you want to read (process). But since our bookshelf (RAM) can only hold a few books (data) at a time, we take pictures 📸 (physical pages) of the pages of the books (data) we want to read (process) later and store these pictures somewhere accessible (disk). When we want to read (process) the stored pages, we can just retrieve the pictures and place them on a shelf in our bookshelf.

This way, by swapping pictures (physical pages) in and out of the bookshelf (RAM/frames), we can manage to read (process) more books (data) than our bookshelf (RAM) could hold at once! 📚➡️📸➡️🔄.

Explaination Physical Memory, Physical Frame, and Physical Page 📚 🧠

Let's imagine the physical memory (RAM) as a big storage shelf, the frames as individual storage bins on that shelf, and the physical pages as the actual content (data) we store in those bins.

+---------------------------------------------------------------+
|                          Physical Memory                       |
|                                                               |
|    +------+     +------+     +------+     +------+     +------+   
|    |Frame |     |Frame |     |Frame |     |Frame |     |Frame | 
|    |  1   |     |  2   |     |  3   |     |  4   |     |  5   |  
|    +------+     +------+     +------+     +------+     +------+    
|      ||           ||           ||           ||           ||
|      \/           \/           \/           \/           \/     
|    +------+     +------+     +------+     +------+     +------+ 
|    |Physical|   |Physical|   |Physical|   |Physical|   |Physical| 
|    | Page  |   | Page  |   | Page  |   | Page  |   | Page  | 
|    |  1   |   |  2   |   |  3   |   |  4   |   |  5   | 
|    +------+     +------+     +------+     +------+     +------+ 
+---------------------------------------------------------------+

  • Physical Memory: It's the entire storage shelf. In our example, it's divided into 5 individual storage bins (though real RAM would have many, many more).

  • Frames: These are the individual storage bins labeled "Frame 1", "Frame 2", etc. They each hold a certain amount of data. If each frame represents, for instance, 4KB of memory, that is the maximum amount of data they can store.

  • Physical Pages: Represented below the arrows, these are the actual snapshots of data stored within each frame. "Physical Page 1", "Physical Page 2", etc., represent chunks of data that are stored in the frames above them. In a real system, the OS controls the swapping of pages in and out of frames to ensure that the processor always has access to the data it needs.

To further illustrate, if data from Physical Page 2 is requested but isn't currently in a frame (perhaps it was swapped out for other data), the operating system will perform a page swap, bringing the needed data back into a frame while moving other data out to ensure the processor can access it quickly and efficiently.