Only 3348 MB of a 4 GB memory?

["Jared C. Davis" <jared@xxxxxxxxxxxxx>]

Hi,

I just installed a 4 GB memory (2 x 2 GB chips), but /proc/meminfo
shows only 3348924 kB installed.  I am using: Linux ivan
2.6.20-15-generic #2 SMP Sun Apr 15 06:17:24 UTC 2007 x86_64
GNU/Linux.

I looked on Google to try to get ideas, and it sounded like my BIOS
might be doing something bad with "MTRRs" and "E820s", but I don't
know what these are.  It's a Dell Dimension 5150, which I think has a
945G chipset but I'm not sure.

Some other people with similar problems posted this kind of output:

jared@ivan:~$ dmesg | grep e820
[    0.000000]  BIOS-e820: 0000000000000000 - 00000000000a0000 (usable)
[    0.000000]  BIOS-e820: 00000000000f0000 - 0000000000100000 (reserved)
[    0.000000]  BIOS-e820: 0000000000100000 - 00000000cfe88c00 (usable)
[    0.000000]  BIOS-e820: 00000000cfe88c00 - 00000000cfe8ac00 (ACPI NVS)
[    0.000000]  BIOS-e820: 00000000cfe8ac00 - 00000000cfe8cc00 (ACPI data)
[    0.000000]  BIOS-e820: 00000000cfe8cc00 - 00000000d0000000 (reserved)
[    0.000000]  BIOS-e820: 00000000f0000000 - 00000000f4000000 (reserved)
[    0.000000]  BIOS-e820: 00000000fec00000 - 00000000fed00400 (reserved)
[    0.000000]  BIOS-e820: 00000000fed20000 - 00000000feda0000 (reserved)
[    0.000000]  BIOS-e820: 00000000fee00000 - 00000000fef00000 (reserved)
[    0.000000]  BIOS-e820: 00000000ffb00000 - 0000000100000000 (reserved)

And looking at that, I can see "holes" such as 0xd0000000 through
0xf0000000 which is a pretty large chunk of memory (524 MB).  I saw
some people who had been able to use mem=4096MB when booting up to fix
their issues after changing some settings in their bioses, but my BIOS
apparently has no configurable settings for memory and when I try to
use this option, my machine appears to be frozen right as it tries to
boot up -- I don't even see any bootup messages, just a blank screen
and a blinking cursor.  I let it blink for about five minutes before I
gave up on it.

I'm wondering what might cause this, and if there's anything I can try
to do to fix it and get the whole 4 GB, or at least more of the 4 GB?

Thanks,
   Jared

--
Jared C. Davis <jared@xxxxxxxxxxxxx>
3600 Greystone Drive #604
Austin, TX 78731
http://www.cs.utexas.edu/users/jared/
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