Three out of Four Isn't Bad

[Néstor]

I have a situation where I have 36 Gigs of ram on a machine and I could only
see 4 Gigs
then I installed the PAE kernel and I can only see 24 Gigs.  I have a ticket
opened with
Red Hat to see what they recommend.

:-)

On Thu, Apr 17, 2008 at 6:00 AM, Bill Davidsen <davidsen at tmr.com> wrote:

> Roger Heflin wrote:
>
> > Dennis Gilmore wrote:
> >
> > > On Wednesday 16 April 2008, Bill Davidsen wrote:
> > >
> > > > I just popped another 2GB in my development machine, 2GB to 4GB RAM,
> > > > and
> > > > only 3GB shows. Yes I looked at the 820 output, yes I tried PAE
> > > > kernels,
> > > > yes I checked the BIOS to see the the hole options were tried, other
> > > > thoughts.
> > > >
> > > > FC6 running 2.6.22.14-72.fc6PAE, also 2.6.24.4 kernel.org build.
> > > >
> > > > dmesg hopefully attached if it doesn't get stripped again.
> > > >
> > >
> > > I have a Dell D820 and while its a 64 bit system,  it has a 32 bit
> > > chip in there somewhere so i can only use 3.25gb of thr 4gb that is
> > > installed could very well be a hardware limitation somewhere.
> > >
> > > Dennis
> > >
> > >
> > Actually, since most OSes are 32bit (read Windows) none of the bios
> > makers set things up  so that the missing ram can be remapped over 4GB since
> > that would be useless under windows.    So they just waste the memory
> > generally, though sometimes there is a bios option to set things to
> > non-windows OS, or change the memory mapping that will allow more to be
> > used, but generally that is only with the higher end machines and even there
> > (where a large number of the machines are used with 64bit OSes) the options
> > don't always exist.
> >
> > On a normal desktop system generally you are out of luck and will at
> > best get maybe 3.2-3.5 GB of ram out of 4GB, and sometimes less depending on
> > how well be bios was setup.    The older the motherboard is the worse it
> > gets.
> >
> > My 3 year old intel board lets me use 2.8GB out of 3GB, I am not sure
> > how bad it would get if I added another GB, I would expect to at best get
> > maybe .5 GB more.
> >
> > Do a "cat /proc/mtrr" to get a better idea of what the bios is telling
> > linux to do.
> >
> > Mine looks like this:
> >
> > reg00: base=0x00000000 (   0MB), size=4096MB: write-back, count=1
> > reg01: base=0xb0000000 (2816MB), size= 256MB: uncachable, count=1
> > reg02: base=0xc0000000 (3072MB), size=1024MB: uncachable, count=1
> >
> >  Actually the BIOS passes the information on memory to the kernel in the
> e820 table, physical memory description. MTRR is set by the kernel. In my
> case (from the original dmesg):
>
> BIOS-provided physical RAM map:
>  BIOS-e820: 0000000000000000 - 000000000009fc00 (usable)
>  BIOS-e820: 000000000009fc00 - 00000000000a0000 (reserved)
>  BIOS-e820: 00000000000e4000 - 0000000000100000 (reserved)
>  BIOS-e820: 0000000000100000 - 00000000c77a0000 (usable)
>  BIOS-e820: 00000000c77a0000 - 00000000c77ae000 (ACPI data)
>  BIOS-e820: 00000000c77ae000 - 00000000c77e0000 (ACPI NVS)
>  BIOS-e820: 00000000c77e0000 - 00000000c7800000 (reserved)
>  BIOS-e820: 00000000ffb80000 - 0000000100000000 (reserved)
>
>  So 4GB total could be useable, but 256MB has been labeled uncacheable for
> > something and 1024MB more is also labeled uncacheable, so with an actual 4GB
> > I may not have any more memory than with 3GB of ram installed with this MB.
> >
> >                                   Roger
> >
> >
>
> --
> Bill Davidsen <davidsen at tmr.com>
>  "We have more to fear from the bungling of the incompetent than from
> the machinations of the wicked."  - from Slashdot
>
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