On Fri, 9 Mar 2007, David Laight wrote:

> On Fri, Mar 09, 2007 at 04:52:35PM -0500, Derrick Lobo wrote:
>> I have been scratching my head on this one for a week....
>>
>>
>> I have a supermicro 5014c-m8b, it has an intel P dual core 531J  3Ghz
>> processor with 4GB ram, the bios shows 4GB however dmesg show 3GB, I
>> installed Red Hat and had the same issue. If I take off 1GB from the
>> server the bios and dmesg match....
>>
>> As per specs from Supermicro the server can take up to 8GB ram. I called
>> supermicro and they claim that the chipset does not support memory
>> remaping, and that other resources are utilized by subsystems such as
>> I/O and PCI Express.
>
> The 'problem' is that part of the 32bit physical address space is used
> for memory-mapped IO (eg it lets you access your PCI cards).
> So you can't map memory to the entire 4GB of address space.
> Typically the top 512MB or 1GM is reserved for mapping IO devices,
> leaving you with 3.5GB or 3GB of memory.
> Some motherboards/chipsets will map the unallocated memory above the 4GB
> boundary.  However that is only accessible if the kernel supports PAE
> (which netbsd doesn't), or you have a 64bit cpu.
> In any case it appears your motherboard doesn't do that.

 	For reference the most memory I've had reported under NetBSD/i386
 	was 4160024576 (3967MB). That was on an asus A8V Deluxe. Based on
 	BIOS revision and video card I've had as low as 3775MB on the same
 	model board...

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 		David/absolute       -- www.NetBSD.org: No hype required --