Some questions come from calculating page table entry and page size.
So, we are discussing how to calculate page table entry with a method:
Let consider a question:
In a system with a 24-bit virtual address and 32KB page size, use a single-level page table. Calculate the page table entry size.
Solution:
Here, Virtual Address = Logical Address = 24 bit, so, Virtual Address Space (VAS) = Logical Address Space (LAS) = = 16MB and page size = 64KB =
So, we can calculate
Let page table entry = e.
Now, we know Page Table Size (PTS) = Number of pages × e
As we know frame size is always the same as page size i.e. page size = frame size = 4KB = .
Now, in a single level paging system Page Table Size (PTS) is always same or less than a frame size otherwise we cannot load this page table into a single frame of main memory.
So, PTS < frame Size (FS) or Page Size (PS)
Then
Another Example:
Question:
A computer system supports 32-bit virtual addresses as well as 256KB page size with the use of a single-level page table. Page table entry size is less or equal to
(A) 16 B (B) 32B (C) 64B (D) 256B
Solution:
Here, Virtual Address = Logical Address = 32 bit, so, Virtual Address Space (VAS) = Logical Address Space (LAS) = = 4GB and page size = 256KB =
So, we can calculate
Let page table entry = e.
Now, we know Page Table Size (PTS) = Number of pages × e
As we know frame size is always the same as page size i.e. page size = frame size = 4KB = .
Now, in a single level paging system Page Table Size (PTS) is always the same or less than a frame size otherwise we cannot load this page table into a single frame of main memory.
So, PTS < frame Size (FS) or Page Size (PS)
Then
So, option (B) is correct.