The Linear Address Space

From: Cameron Gibbs (odly_at_hotmail.com)
Date: 04/27/04 

Date: Tue, 27 Apr 2004 07:43:16 +0000 (UTC)

Hey people.

I have been working through the IA-32 Software Developer's Manuals. I have
read pretty much all of it in some detail (skipping mostly just tables and
lists that can be referenced as needed). Still there is something very basic
in my understanding that is lacking.

There is a Physical Address Space of 4GBytes (2^32 bytes) which basically
identifies all of the binary numbers that can be used as addresses for
assembly language programming.
With the 36-bit address extensions it is possible to increase this to
64Gbytes.
The problem is that in a computer there is Hard Drive storage, RAM storage
and a heap of other devices and the like that all require byte addresses.
Say for example you had a 180GByte HDD in your system, even with the 36 bit
address extension mechanisms which bring the Physical Address Space up to
64GBytes, there are still just not enough Logical Addresses to reference the
whole of the addresses on a system.

Also with Hard Drive partitions and with every program having to be put in a
particular spot on the Hard Drive, it is a very rare thing that one would
write a program that is to be put at address zero.
>>From all this I have come to think that the Linear Address Space is simply
an abstraction or a virtualization of the true state of all of the addresses
within a computer so what I need to know is how are these abstractions that
are used in a program "mapped" to the real addresses of the computer?
How does this work?

Also, I think that paging has something to do with RAM management and the
"checking in" and "checking out" of data to and from RAM but frankly I can
neither confirm nor deny this and hence I just cannot figure out what is
actually going on with paging.
Am I on the right track with paging? - Please correct!

Might the mapping to real addresses have something to do with the Page
Directory Base Register (PDBR) which is Control Register 3 (CR3)?

All help appreciated.

Cameron. 

--
______________________________
Reply to the group.
______________________________
Procedurized mind at work.
       Adhere to the sequence.
The PC & Electronic Data Map Project:
http://members.dodo.com.au/~cameron111
---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.658 / Virus Database: 421 - Release Date: 4/9/04

Relevant Pages

  • Re: PRIMES comparision
    ... beyond that the paging service starts ... Additional RAM gave the added ... the added complexity of NT slows down regular application code, ...
    (alt.lang.asm)
  • Re: Any Reason To NOT Clear Paging File on Reboot?
    ... I have 1GB of RAM, and have completely ELIMINATED the paging file!!! ... Once you start hitting the paging ... If our systems had UNLIMITED memory, we wouldn't even need a paging ...
    (microsoft.public.windowsxp.general)
  • Re: The Linear Address Space
    ... controller to read the data into physical memory (RAM). ... > Am I on the right track with paging? ... used as an offset into that frame. ...
    (comp.lang.asm.x86)
  • Re: What is Page Pooling?
    ... I imagine it refers to paging. ... it allows you saving RAM space. ... (i.e your image is splitted in differents .bin files). ...
    (microsoft.public.windowsce.platbuilder)