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4GB and clock limits on A8N-VM

Last response: in Motherboards
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March 27, 2006 4:14:34 AM

Hi,

I posted a similar message on the "memory" forum but I think my understanding was not correct.
2 Problems:
1) I have 4GB of RAM. The BIOS used to report all 4096MB clocked at 400MHz. Now it shows only 2960MB.
2) The 2960MB are now clocked at 333MHz.

While trying to understand what happened, I stumbled upon this:
http://forums.anandtech.com/messageview.cfm?catid=29&th...

It says that the memory speed is tied to how much memory you have. Th emore memory, the weaker the signales get, the slower the BUS may be. In my case, with 4GB I can't go faster than 333MHz.
Unless I was drunk, I remember clearly that the speed was 400MHz. So I don't have explanation for the 333MHz and for the 2960MB (instead of 4096). On th e4096 I'm sure: I was SO looking forward to see BIOS spit out a number larger than 512 ...

So here are some questions for this forum:
1) are you aware of DDR speed limitations when 4GB (4 dual-sided DIMM) are used?
2) do you have any clue of why the max memory available is 2960MB only now? I run memtest86 for several hours on each DIMM individually and on pairs: no problems (and clock always on 400MHz). I doubt it's the memory. I tried to use all the slots on the MoBo: no problems UNLESS all 4 modules where installed. So this may be a limitation of the architecture. But then again, why all of a sudden???
3) what type of SW/HW tests can I run to determine with certainty (or max likelihood) what's faulty in this system?
4) anybody else has an A8N-VM and is experiencing something similar?

Thanks ...

More about : 4gb clock limits a8n

a b V Motherboard
March 29, 2006 1:03:39 AM

The reason you only get 3GB instead of 4 is due to 32 bit Windows. It can only access a total of 4GB memory addresses. Take out your shared video memory and the address space needed by drives and peripherals and 3GB is not unusual, though it is on the low end. If you run 64 bit Windows you will see all 4 gigs less just the allocated shared video memory for running integrated graphics.
The 333MHz issue I have heard of before, but can't remember the fix.
March 29, 2006 2:27:00 AM

I don't think it's Windows.
I know Win XP does not see all 4GB but that's not the problem.
The BIOS itself does not see 4GB and when I run memtest86 (which is OS-independent) that too sees only 2960MB (which is what the BIOS sees).

I read that most motherboards have some "hidden" limitations when using 4GB: 1GB modules have chips on 2 sides (amny 512MB do too) and having 4 double-sided modules increases the resistance on the bus line that causes the frequency to drop from 400MHz to 333MHz.

You can read more here:
http://forums.anandtech.com/messageview.cfm?catid=29&th...

This would explain why the clock drops ONLY when 4 modules are installed.
With 3 modules the system runs slow but the clock is set at 400MHz. The user manual does not list 3 modules as recommended configuration (but it does not say that it's forbidden).
Still, I can't explain why it used to run at 400MHz and now it goes only to 333MHz (unless I always missed it) but most important I can't explain why it does NOT show 4096 in the BIOS which I know it used to.

I have set the "memory hole" in the BIOS and the RAM was bumped up to 4013 (weird number ...) but the system won't boot. Not even memtest86 would boot from floppy disk.
Removing the "memory hole" brings th ememory back to 2960MB and bootable.

The irony is that with "only" 2960MB Win XP Home (32 bit) works pretty stable while when I had all 4GB it crashed all the times ...

I have not heard from Asus yet: I hope they can cast some light.
I'm tempted to return 2GB since they were pretty expensive and it looks like they slow down the system overall (my system). Seems to me that consumer products are not ready for 4GB yet. Pretty disappointing. BTW: the issue with the bus speed and 4GB is common to many MoBos (search for "4GB RAM 333" on Google).
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April 3, 2009 5:59:33 PM

I have a similar issue: Asus A8N-VM and I have recently added 2 more GB of Corsair dual-channel memory bring my system up to 4GB which the bios sees. When I boot to XP Pro, it only sees 2GB. I added the /PAE switch to the boot.ini and it seems much faster but still only shows 2GB. However, it does say PAE enabled below the 2GB listing.

I am going to see about tweaking the bios a bit because I should be able to get at least 3.5 GB to show in XP.
April 9, 2009 12:08:04 AM

derekge said:
I have a similar issue: Asus A8N-VM and I have recently added 2 more GB of Corsair dual-channel memory bring my system up to 4GB which the bios sees. When I boot to XP Pro, it only sees 2GB. I added the /PAE switch to the boot.ini and it seems much faster but still only shows 2GB. However, it does say PAE enabled below the 2GB listing.

I am going to see about tweaking the bios a bit because I should be able to get at least 3.5 GB to show in XP.


I have the a8n-vm and just added 2 more gig of cosair ram for a total of 4 gig same problem w/ xp and vista 32 bit . Have you found out why?
a b Ĉ ASUS
a b V Motherboard
April 9, 2009 11:55:33 AM

The OP's problem seems to be that motherboard not being able to handle 4 Dimms of RAM stable. It doesn't seem to be the 32-bit limitation for him.
May 16, 2009 4:43:13 PM

I ran into the same problem using the A8N-VM board, even when I upgraded to a 64bit OS. Enable the memory hole remapping feature in the BIOS. Your manual should help you find it.
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