Re: Only 3.2G ram out of 4G seen in an i386 box

From: gmu 2k6
Date: Fri Aug 11 2006 - 07:08:19 EST

On 8/10/06, Simen Thoresen <simentt@xxxxxxxxxxxxx> wrote:
gmu 2k6 wrote:
> so what does it mean that one of Xeons here shows me the full 4GiB as
> total physical memory via `free`?
> btw, the box I'm getting will have the 975X chip and include 4GiB RAM
> and if I understood the problem correctly even with 3GiB there will be
> some memory lost to mapping-issues besides the HI/LO mem
> kernel-reserving issue.
> this is what I get on ia32 P4 with 3GiB
> total used free shared buffers cached
> Mem: 3116108 2608196 507912 0 246652 2039708
> and this is what I get on ia32 Xeon with 4GiB
> total used free shared buffers cached
> Mem: 4087660 268828 3818832 0 57168 103568

Hi Gmu,

This is a bit divergent from the discussion, but will hopefully provide some

The hardware my employer manufactures asks the BIOS to reserve several
largeish ranges (16M and 16M to 512M), and it's been used in various HPC
projects where machines typically have a lot of memory installed.

From my experience, most pre 750x-P4-Xeon chipsets did not support any kind
of memory remapping, so often the top 0.5-1.5G of ram would be 'lost'. Great
Since then, this functionality has started appearing, more or less randomly.
I believe it should be present on all later 75xx chipsets (probably the Core
2 Xeon chipsets as well), but implementation depends on the BIOS (ie the
motherboard vendors), and their grasp of what people do with their boards is
often quite limited.

On the P4 boards (and again the Core 2 boards as well), this is probably
even less ordered as they are 'desktop' boards rather than the more costly
'server' boards.

I'm pretty sure the Athlon64 and Opteron CPUs should support this, but they
too depend on BIOS functionality to rearrange the memory tables.

Just out of interest - what chipset does your Xeon system use?

lspci of the P4 32bit desktop with 3GiB
00:00.0 Host bridge: Intel Corporation 82875P/E7210 Memory Controller
Hub (rev 02)
00:01.0 PCI bridge: Intel Corporation 82875P Processor to AGP
Controller (rev 02)
00:1d.0 USB Controller: Intel Corporation 82801EB/ER (ICH5/ICH5R) USB
UHCI Controller #1 (rev 02)

lspci of the Xeon 32bit HP Proliant Server with 4GiB:
00:00.0 Host bridge: Intel Corporation E7520 Memory Controller Hub (rev 0c)
00:02.0 PCI bridge: Intel Corporation E7525/E7520/E7320 PCI Express
Port A (rev 0c)
00:06.0 PCI bridge: Intel Corporation E7520 PCI Express Port C (rev 0c)
00:1d.0 USB Controller: Intel Corporation 82801EB/ER (ICH5/ICH5R) USB
UHCI Controller #1 (rev 02)

lspci of the new box with 975X and Core 2 Duo not available yet for
obvious reasons (I don't have the the box yet).
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