paging

Question

Can anyone diagrammatically explain what is the difference between Page size vs Page table entry size in a page table?

Comments

Let me try to explain again:

The page table is a data structure used by the operating system to manage virtual memory. It is essentially a table that contains one entry for each virtual memory page, and each entry contains information about that page, such as its location in physical memory or on disk.

The page table must reside entirely in physical memory in order for the system to function properly. This is because the operating system needs to be able to access the page table quickly in order to manage virtual memory. If the page table is too large to fit in physical memory, then the system will not be able to use virtual memory effectively.

Virtual memory is a technique that allows a system to use a larger virtual address space than the available physical memory. This is done by storing some of the virtual memory pages on disk and only loading them into physical memory as needed. However, the page table itself must still reside entirely in physical memory, and the size of the physical memory determines the maximum size of the page table.

In summary, the physical memory cannot be smaller than the page table size, as the entire page table must reside in physical memory in order for the system to function properly. Virtual memory can be used to allow a system to work with a larger virtual address space than the available physical memory, but it does not change the requirement that the page table must be entirely contained within the physical memory. I hope this helps! Let me know if you have any other questions.

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@Aditya_   

In the scenario you described, the page table would not actually contain one entry for each 4KB block of memory, as that would result in a page table that is much larger than the available physical memory. Instead, the page table would only contain entries for the virtual memory pages that are currently being used by the system.

For example, if the system is only using one 4KB block of virtual memory, then the page table would only contain one entry for that page. In this case, the page table would be much smaller than 128KB, and it could potentially fit entirely within the available 4KB of physical memory.

The use of paging in this scenario is to allow the system to use more virtual memory than the available physical memory. By using a page table to manage the virtual memory pages, the system can store some of the pages on disk and only load them into physical memory as needed. This allows the system to use a larger virtual address space than the available physical memory, which can improve the performance and efficiency of the system.

In summary, if a system has 4KB of physical memory and a page size of 4KB, the page table would only contain entries for the virtual memory pages that are currently being used by the system. The use of paging in this scenario is to allow the system to use more virtual memory than the available physical memory, and the page table is used to manage the virtual memory pages.

 

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@rsansiya111 Have you seen at least most of the PYQ questions on virtual memory? If not please solve them before answering such questions. 
https://github.com/GATEOverflow/GO-PDFs/blob/main/Volume-3.pdf

Answer 1

In a page table, the page size is the size of each page of memory that is stored in the page table. The page table entry size is the size of each entry in the table that corresponds to a memory page.

Here is a diagram to illustrate the difference between page size and page table entry size:

Page Table:

Page Table Entry 1	Page Table Entry 2	Page Table Entry 3	...
Page 1	Page 2	Page 3	...

 

 

In this example, the page size is the size of each page of memory (Page 1, Page 2, Page 3, etc.), and the page table entry size is the size of each entry in the page table (Page Table Entry 1, Page Table Entry 2, Page Table Entry 3, etc.).

The page size is typically larger than the page table entry size, as the page table entry size is only required to store the necessary information to locate and access the page of memory, while the page size is the actual size of the page of memory that is stored in the page table.

For example, the page size may be 4KB (4,096 bytes), while the page table entry size may be only 4 bytes. This means that each page of memory is 4KB in size, but each entry in the page table is only 4 bytes in size, and contains the necessary information to locate and access the corresponding page of memory.