Re: address limitation

[Jim Nelson <james4765@verizon.net>]

Ankit Jain wrote:

>hi
>
>well i am not able ot understand this... there are lot
>many more problems
>
>/proc/iomem
>00000000-0009fbff : System RAM
>0009fc00-0009ffff : reserved
>000a0000-000bffff : Video RAM area
>000c0000-000c7fff : Video ROM
>000f0000-000fffff : System ROM
>00100000-077effff : System RAM
>00100000-00250d5b : Kernel code
>00250d5c-0034ac43 : Kernel data
>
>this is just a brief..... System RAM what does that
>mean? the range can just point 65K of RAM? what about
>rest? so what that means?
>  
>

Okay,

00000000-0009fbff : System RAM

This is the 640 KB that is part of the legacy support for real-mode PC 
applications.

0009fc00-0009ffff : reserved
000a0000-000bffff : Video RAM area
000c0000-000c7fff : Video ROM
000f0000-000fffff : System ROM


This is the BIOS and VGA address area (up to 1 MB), once again to 
support real-mode PC stuff (DOS, primarily).  The original IBM PC's (I 
think starting with the XT, maybe the PC) had a 20-bit memory addressing 
scheme, but only 16-bit registers.  If you ever want to hop into the 
way-back machine to the days of CGA's, hardcards, and 5 1/4" floppies, 
grab a book on DOS programming - FreeDOS (http://www.freedos.org) is 
still out there, and it's actually kind of fun to run something that 
blindingly simple :)

00100000-077effff : System RAM


Here is the rest of your system's memory.


>also,
>
>on a 32 bit proceesor we can at the most have a access
>to 4GB of area as we have that many address space.
>well some what it look stupid but then also asking
>some where this blunder i have to clear, that how it
>access the hard disks which is of much high capacity?
>  
>
Hard disks are controlled by sending requests to and from the drive for 
blocks of data.  Sort of like reading a book - you only see a couple of 
pages at a time, but you can access the whole book, or any section of 
it, by flipping to the right page number.  Same way with the hard disk 
controller.  Ask it for sector 11432, and it will give it to you 
(oversimplified, but essentially correct).


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