P4C800-E/Deluxe memory issue with 4 x 1Gb sticks.

[Phil Vossler]

I've tried installing four sticks of 1Gb Crucial DDR modules in two of
these Asus motherboards and each time only 2.94Gb is recognized by the
system. Bios is v1016. The modules are those recommended by Crucial
(CT12864Z40B)

Has anyone else had problems running this board with the maximum memory
possible? Conversely, has anyone had success with this board and the
recommended Crucial memory modules?

First time I've ever had a problem using an Asus board...any assistance
appreciated...

 

[Philip Callan]

I've tried installing four sticks of 1Gb Crucial DDR modules in two of
these Asus motherboards and each time only 2.94Gb is recognized by the
system. Bios is v1016. The modules are those recommended by Crucial
(CT12864Z40B)

Has anyone else had problems running this board with the maximum memory
possible? Conversely, has anyone had success with this board and the
recommended Crucial memory modules?

First time I've ever had a problem using an Asus board...any assistance
appreciated...

When you say 'recognized by the system' do you mean the Motherboard
doesn't recognize it (like at post, it only memory tests 3gb worth) or
the OS?

If the board isn't seeing it, double check your seating, to make sure
their installed firmly.

What speed are you trying to run them at?

You know that it will only operate DDR400 Dual Channel with 2GB or less
RAM, and that if you install more than 2GB, it will drop down to DDR320
dual channel to address the larger amount.

 

[Paul]

I've tried installing four sticks of 1Gb Crucial DDR modules in two of
these Asus motherboards and each time only 2.94Gb is recognized by the
system. Bios is v1016. The modules are those recommended by Crucial
(CT12864Z40B)

Has anyone else had problems running this board with the maximum memory
possible? Conversely, has anyone had success with this board and the
recommended Crucial memory modules?

First time I've ever had a problem using an Asus board...any assistance
appreciated...

Page 118 of the 875P Northbridge chipset shows the memory map:
http://developer.intel.com/design/chipsets/datashts/25252501.pdf

The Northbridge lives within a 4GB address space. AGP and PCI card
requirements come out of the same memory space. The TOMM register
in the Northbridge "punches a hole" in the DRAM, to make room for
the rest of the memory map.

To make more main memory available, try removing PCI cards,
disabling unused PCI onboard devices, decrease the AGP aperture
setting, use a PCI video card with small onboard memory, and maybe
the free memory will be able to reach 3.5GB.

HTH,
Paul

 

[Philip Callan]

Page 118 of the 875P Northbridge chipset shows the memory map:
http://developer.intel.com/design/chipsets/datashts/25252501.pdf

The Northbridge lives within a 4GB address space. AGP and PCI card
requirements come out of the same memory space. The TOMM register
in the Northbridge "punches a hole" in the DRAM, to make room for
the rest of the memory map.

To make more main memory available, try removing PCI cards,
disabling unused PCI onboard devices, decrease the AGP aperture
setting, use a PCI video card with small onboard memory, and maybe
the free memory will be able to reach 3.5GB.

HTH,
Paul

So you're saying that there is no difference between running 3 1G sticks
and running 4 on a 875P chipset? Does it take that RAM out of the
address space total (all 4G) or just the top (xMB) from real RAM I've
never noticed any reduction in total visible memory on any of these
boards I've installed 2GB on.

Or will running the 4th stick just allow you to run all your (visible)
RAM in dual channel?

 

[Paul]

So you're saying that there is no difference between running 3 1G sticks
and running 4 on a 875P chipset? Does it take that RAM out of the
address space total (all 4G) or just the top (xMB) from real RAM I've
never noticed any reduction in total visible memory on any of these
boards I've installed 2GB on.

Or will running the 4th stick just allow you to run all your (visible)
RAM in dual channel?

For max economy, you could run 2x512+2x1024, and the two address
spaces probably wouldn't bump into one another. Running 4x1024 minus
at least 512MB for that PCI/AGP stuff, leaves you with 3.5GB on a
good day, and unless you need that extra bit of ram badly, might not
be a wise investment.

When using 4x512, the 2GB from low memory space doesn't get to bump
into the 512MB+ needed near the top end of the address space. Note
that the Asus BIOS controls this allocation, and if you read the
875P datasheet, no where near that amount of address space needs
to be wasted. I suppose it might depend on whether the Asus BIOS
makes a fixed allocation for the PCI cards (as opposed to examining
each card for its requirements) etc. I don't know enough about
PCI/AGP addressing to be able to say more than that. I mean, there
are standards for this stuff, and maybe Asus follows what some
standard says ?

HTH,
Paul

 

[Alan Howard]

For max economy, you could run 2x512+2x1024, and the two address
spaces probably wouldn't bump into one another. Running 4x1024 minus
at least 512MB for that PCI/AGP stuff, leaves you with 3.5GB on a
good day, and unless you need that extra bit of ram badly, might not
be a wise investment.

When using 4x512, the 2GB from low memory space doesn't get to bump
into the 512MB+ needed near the top end of the address space. Note
that the Asus BIOS controls this allocation, and if you read the
875P datasheet, no where near that amount of address space needs
to be wasted. I suppose it might depend on whether the Asus BIOS
makes a fixed allocation for the PCI cards (as opposed to examining
each card for its requirements) etc. I don't know enough about
PCI/AGP addressing to be able to say more than that. I mean, there
are standards for this stuff, and maybe Asus follows what some
standard says ?

HTH,
Paul

Then there is this issue which I've come across

"Adding extra memory to your PC can slow it down"

http://firingsquad.com/hardware/building_gaming_opteron_2003_Part2/page14.asp