Paging Examples
Assume a page size of 1K and a 15-bit logical address space.
How many pages are in the system?
Paging Examples
Assume a page size of 1K and a 15-bit logical address space.
How many pages are in the system?
How many bits are required to address each byte within a 1024-byte page?
Paging Examples
Assume a page size of 1K and a 15-bit logical address space.
How many pages are in the system?
How many bits are required to address each byte within a 1024-byte page? 10 (2^10 = 1024).
This leaves 5 bits for page number.
So, How many pages are in the system?
Paging Examples
Assume a page size of 1K and a 15-bit logical address space.
How many pages are in the system?
How many bits are required to address each byte within a 1024-byte page? 10 (2^10 = 1024).
This leaves 5 bits for page number. So, How many pages are in the system?
32 (2^5 = 32)
• Now consider a 15-bit address space with 8 logical pages. How large are the pages?
• Assuming a 15-bit address space with 8 logical pages. How large are the pages?
• Answer: 2^12 = 4K. It takes 3 bits to reference 8 logical pages (2^3 = 8). This leaves 12 bits for the page size and thus pages are 2^12.
Consider logical address 2049 and the following page table for some process P0.
Assume a 15-bit address space with a page size of 1K.
What is the physical address to which logical address 2049 will be mapped?
8
0
3
Consider logical address 2049 and the following page table for some process P0.
Assume a 15-bit address space with a page size of 1K.
What is the physical address to which logical address 2049 will be mapped?
8
0
3
Step 1. Convert logical address to binary:
Logical address:
000100000000001
0
1
2
3
4
Logical Pages
8
0
3
Step2. Determine the logical page number:
Since there are 5-bits allocated to the logical page, the address is broken up as follows:
00010 0000000001
Logical page number offset within page
0
1
2
3
4
Logical Pages
Step 3. Use logical page number as an index into the page table to get physical page number.
Logical Address:
00010 0000000001
00010
8
0
3 00011
Step 4. Concatenate offset with physical page frame number
Logical Address
00010 0000000001
00010
8
0
3 000110000000001
8
0
3
P0.1
2048
1024
0
3072 P0.2
4096
000110000000001 = 3073
0
1
2
3
4
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