Question

How to calculate a physical address given a virtual address

Asked by: namsu55

I am having problems understanding how to calculate the Physical address given the Virtual address.

Here is a question from the Operating Systems, 3/e book from Deitel:

At an instant in time a computer has a page table of which a part (entries 1086, 1087,
1088 decimal, with numbering starting at 0) is shown in Table 2. Given that the page
size is 4096 bytes, compute the physical address for virtual address 43d5bc.

Table 2

-------
...
5c
4e
fc
...

-------

Can somone explain to me in steps how it is done?

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Asked On
2008-05-19 at 20:38:44ID23415997
Tags

Virtual Memory Calculation

Topics

Operating Systems Miscellaneous

,

Miscellaneous

,

Operating Systems Development

Participating Experts
1
Points
500
Comments
6

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Answers

 

by: sunnycoderPosted on 2008-05-20 at 03:05:46ID: 21604676

>for virtual address 43d5bc.
6X4 = 24 bit address
some bits are page number, others are offset in the page

>Given that the page size is 4096 bytes,
to be able to access each byte in the page, you need 12 bits ... remaining 12 bit page number

  43d                          5bc
Page no                    offset

43d is 1085 in decimal ... so you need contents of page 1085 .... That will give you frame address ... concat frame address and offset - and you have the physical address ...

A grpahical view of the process can be found here
http://williams.comp.ncat.edu/addrtrans.htm

 

by: namsu55Posted on 2008-05-20 at 07:35:01ID: 31459486

Thanks alot for that.

 

by: namsu55Posted on 2008-05-20 at 09:06:47ID: 21607566

I don't quite understand why you had 6 * 4?
and the page size part, if you could explain that to me. The rest is fine. Thanks.

 

by: sunnycoderPosted on 2008-05-20 at 09:33:14ID: 21607839

43d5bc
6 hex digits ... each hex digit is 4 bits

 

by: namsu55Posted on 2008-05-20 at 10:04:31ID: 21608124

So for example:

4 = 100
3 = 11
d = 1101

but the 3 and 4 have 3  and 2 bits, how does that make it four, I appreciate the help Thanks.

 

by: sunnycoderPosted on 2008-05-20 at 21:56:29ID: 21612202

hex to binary relationship is 4 bits  ... thats how they are expressed.
4 = 0100
3 = 0011
d = 1101

20120131-EE-VQP-002

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