One - level page tables for virtual to physical address translation - Operating System

Discussion

• Senam    -Posted on 08 Jan 19
  What is the meaning of one level table?
  And why u assume physical memory 512mb?
• Nirja Shah   -Posted on 18 Nov 15
  - Since the size of the page is too small it will make the size of the page tables huge.
  
  - Size of page table = (total number of page table entries)∗(size of a page table entry)
  
  - Consider an example of the number of entries in the page table
  
  Number of entries in page table = (virtual address space size)/(page size)
  = (2^32)/(2^10)
  = 2^22
  
  - Let us check how big each entry is.
  
  - If the size of physical memory is 512 MB then the number of bits that are required to address a byte in 512 MB is 29.
  
  - So, there will be (512MB)/(1KB) = (2^29)/(2^10) page frames in physical memory.
  
  - 19 bits are required to address a page frame.
  
  - Therefore, every entry in the page table requires to have 19 bits.
  
  - The page table entry also holds the auxiliary information about the page such as the present bit, a dirty or modified bit, address space or process ID information and many others.
  
  - Hence,the size of the page table is
  (total number of page table entries)∗(size of a page table entry)
  (2^22 ∗19) bytes
  9.5 MB
  
  - This much of the memory is required for each process because each process maintains its own page table.
  
  - Size of the page table will be more for physical memory more than 512MB.
  
  - Therefore, it is advised to use multilevel page table for such scenarios.

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