For the following questions, consider a system that has a physical main memory s

Question

For the following questions, consider a system that has a physical main memory size of 32KB (215) and a page frame size (and hence page size) of 4KB (212). Assume that the system uses pure demand paging and that the system supports up to 16-bit logical/virtual addresses. Assume that a process P2 with a logical address space of 64KB (216) executes on this system. Assume that the current state of the page table for P2 in as shown below. The index of each entry in the page table is given for your convenience. Note that both the page and page frame number are in decimal. If a logical page is not currently in the physical main memory, no frame number is specified for that logical page.

Page

Frame

0

1

1

-

2

7

3

2

4

0

5

-

6

5

7

-

8

-

9

3

10

-

11

-

12

-

13

4

14

-

15

6

Question: How many page frames are there in the above pure demand paging memory system? ___________(Your answer should be in exponential form.)

How many bits are needed to represent a physical page frame number in the system? _______________

How many page frames are there in the process P2? _____________(Your answer should be in exponential form. )

How many bits are needed to represent a valid logical page number in the logical address space of process P2? _____________

At any given time, what is the maximum number of entries in the page table of P2 that can have valid physical frame numbers? ____________

Assume that P2 issues the logical address 0xA87A. What is the logical page number contained in the given logical address, in hexadecimal? ___________

What is the page number that corresponds with the hexadecimal logical address of the page being requested in the previous question? ________________

Is this page being requested currently in the physical main memory? (yes or no) _____________

Page

Frame

0

1

1

-

2

7

3

2

4

0

5

-

6

5

7

-

8

-

9

3

10

-

11

-

12

-

13

4

14

-

15

6

Explanation / Answer

For the following questions, consider a system that has a physical main memory size of 32KB (215) and a page frame size (and hence page size) of 4KB (212). Assume that the system uses pure demand paging and that the system supports up to 16-bit logical/virtual addresses. Assume that a process P2 with a logical address space of 64KB (216)


1. Number of page frames are there in the above pure demand paging memory system = >

2^15 / 2^12 = 2^3 = 8 Page Frames

2. For representing 8 ohysical frames we need 3 bits

3. 2^16 / 2^12 = 2^4 = 16 Page Frames

4. Bits that are needed to represent a valid logical page number in the logical address space of process P2: We require 4 bits to represents 16 Frames

5. So now we know that 16 bit of Logical address has 4 bit page number and 12 bit offset

Assume that P2 issues the logical address 0xA87A. What is the logical page number contained in the given logical address, in hexadecimal?

As we know 0xA87A . has 12 bit offset and 4 bit page frame number ,
So 0xA is the  logical page number contained

What is the page number that corresponds with the hexadecimal logical address of the page being requested in the previous question? _______10th Page i.e 0xA

From The Table we can see for 0xA i.e 10 in decimal no frame has been specified.

Is this page being requested currently in the physical main memory? (yes or no) ____NO_______



Thanks, let me know if there is any concern.

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