A8N-SLI DDR 500 a8n sli why does it go auto?

[dhanson865]

These URLs show you a similar BIOS screen to what I'm discussing

http://pics.bbzzdd.com/users/JustAnAverageGuy/CIMG1806.JPG
http://pics.bbzzdd.com/users/JustAnAverageGuy/CIMG1807.JPG

Note those pics are from a Premium and I'm working with a Deluxe so the HT voltage and chipset voltage options don't exist on the system I'm working on.


My problem is that if I change the memory "divider" from 400mhz to anything else the jumperfree screen changes from Manual to Auto.

I have DDR500 so I wan to try settings like these:

Hyper Trnasport Freq - 3x or 4x

CPU Freq - >200mhz no idea how high yet
PCI Express - 100Mhz
DDR Voltage - 2.65 to 2.75
CPU Multiplier - 7, 8, or 9 (avoiding half multipliers)
PCI Clock Syn - 33.33Mhz

Mem clock Index value - 400, 433, 466, 500 (this is the setting that if I change undoes my jumperfree stuff on the other screen)
Cas Lat - 3
Min Ras Active time (Tras) - 8T
Ras - Cas delay (Tred) - 3 or 4
Row precharge time (Trp) - 3 or 4
etcetera

I can easily get the processor and ram to overclock if I leave the memory at 1:1 timings at memory index 400 but I want to find out what the maximum memory throughput can be. I'm trying to get the best performance I can without noticably overclocking the CPU as I want to keep the CPU fan at very low RPMs.

It's also noteworthy that this is my dads system and is normally kept in a house with mulitple pets and gathers quite a bit of pet hair in the case filters so air flow can be comprimised. I can't afford to leave it at the maximum overclock as heat issues will reduce the viability of pushing the edge.

It's not the end of the world if I can't change the memory divider. I can just increase the LDT and overclock the CPU mildly at 1:1 but I'd really like to master all the possibilities and run a few benches before I hand the system off again.

For the curious it is a Antec 835 case with 5x 80mm case fans running at very low voltages with a Seasonic S12-430 powering it all. Cool&Quiet is being used when the multiplier is at 9. Cool and Quiet overrides the multiplier settings so I may or may not leave that enabled if I find a way to run the memory devider at something other than 1:1

 

[dhanson865]

crossposted at http://forums.silentpcreview.com/viewtopic.php?t=30097 in case I can get a response there quicker.

 

[Megatomic]

You don't want to move the Memclock Index from DDR400. Up your HT speed to 250MHz and run the Memclock Index at DDR400 to give you 1:1 between HTT and memory bus speed.

The reason for this is that ASUS did a poor job naming this setting. Memclock Index should have been called divider and they could have used fractions rather than bus speeds. If you select DDR400 in Memclock Index you are really telling the mobo to run the memory at whatever the CPU HTT is.

I can explain in more detail if you need me to.

 

[Megatomic]

Umm, let me clarify something. You can run any HTT you want your CPU to run at, not just 250MHz. If you set the HTT to run at 235MHz and set the Memclock Index to run at DDR400, the memory will run at 235MHz also.

Sorry for the confusion. I initially thought you were wanting to run the CPU at 250MHz specifically.

 

[dhanson865]

I realize I can move the LDT to 250Mhz or anywhere between 200 and 250MHz. The problem is that I want to run at 9x multiplier so that cool and quiet can still be active. At the 9x multiplier I can't get anywhere near the 250MHz without severly overclocking the CPU.

I want to know WHY the bios flips back to AUTO from Manual when I change the Memclock index from DDR400 to anything else. I want to be able to test memory speed changes without overclocking the CPU and without changing the CPU multiplier.

I know you are just trying to help but this is a very specific issue I'm asking about. I'm not just asking how to make the computer run faster...

 

[Megatomic]

So, if you lower Memclock Index to DDR333 it does this too? I have an A8N-SLI Premium and I don't experience this when I go to DDR333. But now that I have DDR500 RAM I don't have to do that anymore. And I've never tried to run Memclock Index faster than HTT.

I guess I just don't know what the problem is with your board. Do you have the latest BIOS installed? And maybe you could describe your reasoning behind wanting to run the memory at a faster bus speed than HTT - that one baffles me.

 

[dhanson865]

Nope, moving it to 333 doesn't cause the problem.

Do you fully understand cool n quiet or have you never used it?

The default multiplier for this CPU is 9. The muliplier is lowered to 5 when idle by cool and quiet and raised back to 9 when at load. If you manually change the multiplier in the bios to 8 or 7 it will boot at that rate, but then cool and quiet will drop the multiplier to 5 at idle and raise to 9 at load shortly after you get in windows.

So yes, I can change the multiplier to 7 or 8 and turn off cool and quiet to get full control over the multiplier but then I lose the energy savings of the lower CPU voltage at idle and the sound savings of lower heat output allowing my fans to run at lower RPM.

Now since my ram can do 500 MHz with no change in sound and only a minimal change in voltage I could theoretically get a small increase in speed in some apps by running the RAM at a high rate.

I already have the fans and heatsink and CPU as fixed items. I am not willing to increase the fan rates or physically change the CPU or Heastsink at this point.

I can increase the LDT and run the CPU at a small overclock without changing the fan rates. Lets assume small is 5%, I haven't determined the actual margin.

I'm now looking for the bios settings that give me the best performance with this given set of limits:

CPU multiplier must be 9x
LDT can't be much above 210

What can I do to increase memory bandwith given those limitations other than change the memory divider?

Why can't I change the divider to a higher value and still maintain control over the CPU speed?

Currently setting the Memory divider to 433 results in severely underclocking the CPU. Same result with 466 or 500 as well.

Assuming I can't use a memory divider other than 1:1 (400) then I'll end up leaving the CPU slightly overclocked and the memory severely underclocked until such time as I buy a different CPU (assuming that a Rev E or Rev F 939 CPU will produce significantly less heat and allow me to run the LDT higher at the same heat output).

 

[Megatomic]

Though I don't use CnQ, I do understand it. Something you may not be aware of is that the performance of AMD A64 chips is not much influenced by memory bandwidth. That is to say that if you run with DDR400 vs DDR433 with only the memory running at the different frequency, there will not be any noticeable real world performance increases. Certain benchmark utilities will show a difference, but games and windows will not show the same increases.

I'm at a loss in being able to help you out in this regards though. Sorry to have taken this off topic.

 

[dhanson865]

I fully understand how minimal the increase in performance is likely to be for the exact configuration I'm trying to reach. I simply want to know why the BIOS doesn't allow me to use those particular memory dividers in this particular case.

The reality is that I can run 200 mhz (DDR 400) at 3-3-3-8 with stock voltage
slightly higher (maybe DDR 420) at 3-4-3-8 with a little extra voltage
and then 3-4-4-8 works all the way up past DDR500 with a higher voltage still.

Having full access to the multipliers would make the difference between running DDR 420 and DDR490 at the same CPU speed and heat level and wouldn't change latency much at all.

In terms of performance it probably is splitting hairs for most apps. If I were really lazy about it I'd just leave cool n quiet on, set the LDT at 205, put the memory at 3-4-3-8 and 2.65v and call it good.