I have a situation where I have 36 Gigs of ram on a machine and I could only see 4 Gigs <br>then I installed the PAE kernel and I can only see 24 Gigs. I have a ticket opened with <br>Red Hat to see what they recommend.<br>
<br>:-)<br><br><div class="gmail_quote">On Thu, Apr 17, 2008 at 6:00 AM, Bill Davidsen <<a href="mailto:davidsen@tmr.com">davidsen@tmr.com</a>> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div class="Ih2E3d">Roger Heflin wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
Dennis Gilmore wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
On Wednesday 16 April 2008, Bill Davidsen wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
I just popped another 2GB in my development machine, 2GB to 4GB RAM, and<br>
only 3GB shows. Yes I looked at the 820 output, yes I tried PAE kernels,<br>
yes I checked the BIOS to see the the hole options were tried, other<br>
thoughts.<br>
<br>
FC6 running 2.6.22.14-72.fc6PAE, also <a href="http://2.6.24.4" target="_blank">2.6.24.4</a> <a href="http://kernel.org" target="_blank">kernel.org</a> build.<br>
<br>
dmesg hopefully attached if it doesn't get stripped again.<br>
</blockquote>
<br>
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.<br>
<br>
Dennis<br>
<br>
</blockquote>
<br>
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.<br>
<br>
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.<br>
<br>
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.<br>
<br>
Do a "cat /proc/mtrr" to get a better idea of what the bios is telling linux to do.<br>
<br>
Mine looks like this:<br>
<br>
reg00: base=0x00000000 ( 0MB), size=4096MB: write-back, count=1<br>
reg01: base=0xb0000000 (2816MB), size= 256MB: uncachable, count=1<br>
reg02: base=0xc0000000 (3072MB), size=1024MB: uncachable, count=1<br>
<br>
</blockquote></div>
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):<br>
<br>
BIOS-provided physical RAM map:<br>
BIOS-e820: 0000000000000000 - 000000000009fc00 (usable)<br>
BIOS-e820: 000000000009fc00 - 00000000000a0000 (reserved)<br>
BIOS-e820: 00000000000e4000 - 0000000000100000 (reserved)<br>
BIOS-e820: 0000000000100000 - 00000000c77a0000 (usable)<br>
BIOS-e820: 00000000c77a0000 - 00000000c77ae000 (ACPI data)<br>
BIOS-e820: 00000000c77ae000 - 00000000c77e0000 (ACPI NVS)<br>
BIOS-e820: 00000000c77e0000 - 00000000c7800000 (reserved)<br>
BIOS-e820: 00000000ffb80000 - 0000000100000000 (reserved)<div class="Ih2E3d"><br>
<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
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.<br>
<br>
Roger<br>
<br>
</blockquote>
<br>
<br>
-- <br></div><div class="Ih2E3d">
Bill Davidsen <<a href="mailto:davidsen@tmr.com" target="_blank">davidsen@tmr.com</a>><br>
"We have more to fear from the bungling of the incompetent than from<br>
the machinations of the wicked." - from Slashdot<br>
<br></div><div><div></div><div class="Wj3C7c">
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