PowerPoint Presentation
Concurrency & Virtual Memory
COMP1411: Introduction to Computer Systems
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Dr. Xianjin XIA
Department of Computing
The Polytechnic University
Spring 2022
These slides are only intended to use internally. Do not publish it anywhere without permission.
How many “Example” output lines does this program print?
void try()
printf(“Example\n”);
int main()
printf(“Example\n”);
Solution to Problem 1
Problem 2: address translation
A main memory (hardware) has size 1MB
A program (virtual memory) has size 16MB
In a paging system, the size of one page is 1KB
How many frames does the main memory contain?
How many virtual pages does the program contain?
How many bits are needed to address a byte in the main memory?
How many bits are needed to address a byte in the virtual memory?
How many bits are needed to address a byte in a page?
Problem 2: address translation
1MB / 1KB = 1024
16MB / 1KB = 16k
Problem 2: address translation
11……1111 = (M-1)10
1M 20 bits
How many bits are needed to address a byte in the main memory?
Problem 2: address translation
16M 24 bits
How many bits are needed to address a byte in the virtual memory?
11……1111 = (M-1)10
Problem 2: address translation
1K 10 bits
How many bits are needed to address a byte in a page?
11……1111 = (M-1)10
Problem 3: address translation
Assume we use 24 bits for an address
Assume the first virtual page/physical page is numbered from 0
Given virtual address 0x000856, which virtual page does this address belong to?
Problem 3: address translation
0, 1, 2, 3, 4, 5, ……, 1023
00..0000, 00..0001, 00..00010, ……, 00..00001111111111
0000……..0000 0000 0000
0000……0011 1111 1111
0000……..0100 0000 0000
0000……0111 1111 1111
0000……..1000 0000 0000
0000……1011 1111 1111
0000……..1100 0000 0000
0000……1111 1111 1111
Problem 3: address translation
Starting address? Ending address?
Problem 3: address translation
Virtual Page 2
0000 0000 0000 1000 0101 0110
Problem 4: address translation
Virtual page 2 is mapped to physical page 5
What’s the physical address of 0x000856?
Problem 4: address translation
00000000000010
0001010110
0001010110
0000000101
Generic address translation
Page offset
Virtual page number
Page offset
Virtual address
Virtual page
number Physical page number
Physical page number
Physical address
Page table
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