P5GD1 Cannot See 4Gb of Memory

  • Thread starter Thread starter tvc
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tvc

I recently purchased an ASUS P5GD1 motherboard and installed 4 Samsung
DDRAM 1GB, PC-3200 DDR400 DIMMs. The BIOS reports only 3200Mb of
memory.

I tried each DIMM individually and they all work. I also tried adding
one at a time and saw 1024Mb, 2048Mb, 3072Mb, and 3200Mb
respectively.

Any ideas?

Thanks.

==============
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I recently purchased an ASUS P5GD1 motherboard and installed 4 Samsung
DDRAM 1GB, PC-3200 DDR400 DIMMs. The BIOS reports only 3200Mb of
memory.

I tried each DIMM individually and they all work. I also tried adding
one at a time and saw 1024Mb, 2048Mb, 3072Mb, and 3200Mb
respectively.

Any ideas?

Thanks.
Click to expand...

I haven't read the 915 datasheet yet, but a typical reason for a
desktop Northbridge to do this has to do with address space. The
PCI/AGP address space comes out of the total 32 bit address space.

Server chipsets that address more than 32 bits, tend to have two
options. They can either leave the hole for PCI/AGP, below the 4GB
mark, or some of them can remap memory or move that space for I/O
higher in the memory map.

You could experiment a bit, by disabling or removing PCI devices,
and see if the size of lost memory changes at all. I don't know what
exact algorithm the BIOS uses - whether it has a fixed allocation
per PCI device, or is using some info from the config space of each
PCI device to decide how much to allocate. PCI devices can either
be plug-in cards or they can be integrated devices (Marvell LAN or
ITE8212F RAID controller ?). Presumably PCI Express consumes address
space like an ordinary PCI card would ?

HTH,
Paul
 
Paul said:
I haven't read the 915 datasheet yet, but a typical reason for a
desktop Northbridge to do this has to do with address space. The
PCI/AGP address space comes out of the total 32 bit address space.
Click to expand...

Interesting. Went to the datasheet and from page 203 and forward Intel
describes this.
As installed system memory approaches 4GB, one can see this behaviour.

I wonder, will it be almost useless to go for 4GB instead of staying with
3GB due to this?
 
"Egil Solberg" said:
Interesting. Went to the datasheet and from page 203 and forward Intel
describes this.
As installed system memory approaches 4GB, one can see this behaviour.

I wonder, will it be almost useless to go for 4GB instead of staying with
3GB due to this?
Click to expand...

"Almost useless" - that sounds like something the marketing team could
use in the ad copy :-)

It would seem that way. Depending on motherboard type, I've seen
reports of 3.2 to 3.5GB available, and that would seem to be a waste
of money. 2x1024 + 2x512 might make more sense, except for those who
need every scrap of memory they can get. For example, if doing
logic simulation, it might pay to use a PCI video card - maybe
removing the AGP from the picture will free up more address
space for use by the ram ? What you do, may depend on how badly
you need the memory.

As there are OS and application issues with that much RAM, the
address space on the Northbridge might not be the only limitation.
Perhaps the fact that only 3.2GB is available isn't all bad,
if say the memory footprint for the system is 0.2GB, and the
OS has a limit of no more than 3GB for a single application.
For people playing with that much ram, there is plenty of
research to do. This post covers some of the issues and the
technical terms used can be used in further Google searches:

http://groups.google.com/[email protected]

Paul
 
Paul said:
It would seem that way. Depending on motherboard type, I've seen
reports of 3.2 to 3.5GB available, and that would seem to be a waste
of money. 2x1024 + 2x512 might make more sense, except for those who
need every scrap of memory they can get. For example, if doing
logic simulation, it might pay to use a PCI video card - maybe
removing the AGP from the picture will free up more address
space for use by the ram ? What you do, may depend on how badly
you need the memory.

As there are OS and application issues with that much RAM, the
address space on the Northbridge might not be the only limitation.
Perhaps the fact that only 3.2GB is available isn't all bad,
if say the memory footprint for the system is 0.2GB, and the
OS has a limit of no more than 3GB for a single application.
For people playing with that much ram, there is plenty of
research to do. This post covers some of the issues and the
technical terms used can be used in further Google searches:

http://groups.google.com/[email protected]
Click to expand...


Very interesting, Paul. I actually learn something here. Thanks for an
informative post.
 
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