Re: address limitation

[Jim Nelson]

Ankit Jain wrote:
Thanks a lot for help
rest inline:)
--- Jim Nelson <[EMAIL PROTECTED]> wrote: 
 

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).
   

thanks again but according to this concepts of pages
if the size is of size 40 GB then size of each page
should be 10kb
is it correct...becaz when only it will be able to map
the complete hard disk....
thanks again
 

Actually, it's 512 bytes - one sector.  As far as I can tell (looking at 
a book I've got) at the most, the IDE controllers can handle a 
read/write request of 256 sectors * 512 bytes = 128 KB.  The actual 
mapping of the hard drive is done at a number of levels.  You have the 
actual hardware addressing scheme (most modern hard drives use a system 
not too dissimilar to SCSI drives), on which you put a partition table 
(to divide the raw disk into chunks), and in each you put a filesystem 
(that keeps track of which chunk of which file is put where).

Different filesystems work in different ways - the FAT filesystem on 
floppies, USB camera memory cards, and DOS/Windows partitions, the 
ext2/ext3 filesystem that is the standard Red Hat filesystem, Reiserfs 
which is standard with SuSE and newer Slackware, and many, many others 
that are used for interoperability with other UNIX variants, or work on 
embedded systems, or work on DVD-ROM, etc.
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