Re: Tyan Thunder K8W S2885 with 4GB memory missing memory??
On Tue, Sep 27, 2005 at 06:37:50AM -0700, Max wrote:
> I'm suffering the same problem on S2875. While is it possible to make Linux
> seeing all 4GB of memory available, that causes kernel traps on attempts to
> use higher memory regions. So I'm forced to live with smaller amount of
> memory visible in favor of system stability.
>
> Max
>
> From the official Tyan FAQ:
>
> ===
>
> Why does my OS see less than the total memory installed when I install 4GB
> or more of memory (typically 512MB less)?
>
> The BIOS needs to overlay the APIC, ACPI Table, AGP Aperture and PCI MMIO
> (Memory-mapped I/O [see PCI Spec 2.3, Section 3.2.2 for more information])
> over the last 512MB of the 4GB physical address space. OS accessible memory
> and these structures cannot both exist at the same place and this portion of
> DRAM is hidden and unavailable to the OS.
>
> Is there a solution for the missing memory when using 4GB of total memory?
>
> Not easily, the theoretical possibility exists that the BIOS can map all of
> the addresses attached to one DIMM module above the 4GB limit, but the BIOS
> cannot move smaller address ranges piece by piece. Mapping a whole DIMM is
> a new concept, unproven in real world testing. It also penalizes 32-bit
> OS's that cannot use more than 4GB. Since the BIOS does not know what OS
> you have when it does the memory assignments, it has to optimize for the
> common case, which is likely a 32-bit OS you may or may not want to use. In
> a system with less than 4GB the BIOS must choose between providing as much
> as possible below 4GB to benefit 32-bit legacy OS users or raise one whole
> DIMM module above the 4GB ceiling to benefit 64-bit OS 's at the loss of
> DRAM to a much more memory limited 32-bit OS.
What a load of crap. They don't have to decide which way to optimize
it. They should let the end user pick that with a bios option just as
almost every other athlon 64/opteron board has done.
Time for them to make a bios update with proper options in it if that is
really the current state of their bios.
Len Sorensen
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