Re: [rhelv5-list] PAE Kernel 32 bit RHEL 5.2 64GB RAM

[Hugh Brown]

My understanding was that it was an addressing limitation. The processor can only address 32-bits worth of hardware and the addresses for memory and pci devices are in the same pool. Way back when, it was decided that devices would be addressed starting at the 2^32 boundary and work backward. Memory got addressed from the low boundary and worked up. When machines finally got 4gb of memory the two met and a portion of memory/ram couldn't be addressed.

Hugh

solarflow99 wrote:

thats interesting, I never came across that before.  I dont know why it
needs to map ram like that, and not just use the video card ram.  That means
if I had a 4GB video card there would be nothing left for me? :)




On Wed, Sep 24, 2008 at 3:07 PM, Sharpe, Sam J <[EMAIL PROTECTED]>wrote:

Because both have different PCI devices?

I think Janne's point is that:

Machine 1: 4096 - 3986 = 110 MB of memory mapped to PCI devices and
unavailable to the OS
Machine 2: 4096 - 3286 = 810 MB of memory mapped to PCI devices and
unavailable to the OS

You don't have Graphics Cards with a total of something like 768MB of
Memory installed in Machine 2 do you? Of course if the machines are
completely identical, then I have no idea.

-----Original Message-----
From: [EMAIL PROTECTED] [mailto:rhelv5-list-
[EMAIL PROTECTED] On Behalf Of solarflow99
Sent: 24 September 2008 15:02
To: Red Hat Enterprise Linux 5 (Tikanga) discussion mailing-list
Subject: Re: [rhelv5-list] PAE Kernel 32 bit RHEL 5.2 64GB RAM

but why does 1 system show 3.2GB and the other 3.9?  they both had 4GB
installed



On Wed, Sep 24, 2008 at 2:59 PM, Janne Blomqvist

<[EMAIL PROTECTED]>

wrote:


      solarflow99 wrote:


              that makes me wonder about something I have several

computers

with 4GB of ram using the regular 32 bit kernel (non-PAE) and I see
different amounts of ram, for instance:
               ]# free -m
                                total      Mem:          3286

]#

free -m
                                total      Mem:          3986



      Probably PCI device memory. They start at 4 GB and go downwards
(AFAIK most are not capable of 64-bit addressing so they have to be

below

4 GB).

      Now, many BIOS:es support "PCI hole remapping" (or whatever it's
called), meaning that the memory that gets clobbered by the PCI

devices

can be remapped to somewhere beyond the 4 GB limit. However, obviously
you'll need PAE or x86-64 in order to access this remapped memory.

      --
      Janne Blomqvist

smime.p7s
Description: S/MIME Cryptographic Signature

_______________________________________________
rhelv5-list mailing list
rhelv5-list@redhat.com
https://www.redhat.com/mailman/listinfo/rhelv5-list