This is from Tony Who works for OCZ
Originally Posted by Tony @ OCZ This is just the start, as I find more I will add to this post.
Tests conducted with 6400 Allendale good to 510fsb using the 7 multi.
OCZ micron dimms (generic ES samples) No fixed product name or SPD
OCZ 600W Evo stream PSU
First tests were to determine how Asus unlocked the board to reach 500+fsb.
From my chipset strap guide we all know that around 370fsb Intels 975/965 chipset starts to have issues if its left on the 1067 strap. Now the fact this 965 based board is doing 500fsb+ means somewhere along the line Asus force a strap change in bios, this means somewhere between 370 and 500+FSB the board loses memory performance.
So I conducted a few easy tests, first graph shows the theory behind how Asus are manipulating the straps without you knowing.
From the graph the blue section shows how the strap should effect the clock on the Northbridge. From 267 fsb (1067 strap) the NB clock rises until 333fsb(1333 strap) where it falls back to default and starts to ramp again as it moves closer to 400fsb (1600 strap if it existed) then it resets again as the fsb moves to 467fsb (1867strap if it existed) Now this all depends on the strap settings being set as they should be, fact is they are not.
So, we then look at the red section of the graph which shows the NB clock rising from 267fsb all the way to 400fsb, this means that Asus has a massive overclock on the northbridge before they reset the strap at 401fsb. Now they have not utilised the 1600 strap as far as we know; at this time it is not known to exist, so the boards sets the 1333 strap. This means the NB instead of completely resetting to its base clock frequency actually resets in an already overclocked state as the reset point was actually 333fsb, but the CPU fsb is already at 401; infact it resets to what should be its max overclock if the straps were actually being set correctly.
From this point the internal latency on the chipset losens even though the chipset its self is overclocked. This allows the chipset clock to ramp up even higher than it did under the 1067 strap. Now the red section of the graph shows what would happen if the straps were reset at the correct strap points if Asus continued the trend of strap manipulation and if the 1600 and 1867 straps were available...issue is they don't seem to be, so we have to now look at the green section of the graph to show what is actually happening on the board.
From the green section we see the NB clock ramps up with the CPU fsb from 267(1067 strap) all the way to 400fsb, where some manipulation occurs, and the board sets the 1333 strap but from a base 400CPU fsb. The NB clock then dips down to around 467fsb; where upon its clock rises higher than was possible on the 1067 strap. From 467fsb the NB is running it's highest internal clock frequency even though it has the slackest latency setting. The increase of clock speed has a positive effect on memory performance bringing it into line with what you see at the highest point NB clock on the 1067 strap, however the cpu is now running much faster than was previously possible under the 1067 strap.
This graph actually shows memory performance compared to actual CPU bus speed set with 4-4-4- timings 1:1. As you see there is a marked dip in memory performance at 400fsb where the chipset clock speed dips, infact you have to go back to 360fsb/1067 strap to see the same performance from the dimms which shows the 1067 strap is MUCH faster than the 1333 on this motherboard. Now the graph is quite linear and around 470fsb you see memory performace now matches whats is seen at the top end of the 1067 strap, the only issue is it is now stable where under the 1067 strap at 399fsb you probably will see some instability issues. From 467fsb onwards you will now see the highest performace from your dimms although you are relying on how good the NB overclocks under the 1333 strap.
Now what I did not show on this latest graph is that from 360fsb to 399fsb the memory was VERY unstable, infact scrolling errors in memtest were the norm in all tests, not just test 5. This proves under the 1067 strap the 965 chipset is hitting the same clock speed limitations as the 975 chipset, the only difference is the board actually still tries to run, on all the 975 boards i have tested once the chipset hits its max clock the boards just give up.
One other thing is 400fsb has an added tweak. 399fsb had memtest bandwidth of 4799MB's but was completely unstable, 400fsb had bandwidth of 4812MB/s and was completely stable... but as soon as I moved to 401fsb bandwidth shot down to 4324MB/s.
This situation reminds me of the old P4P800 turbo mode at 200fsb where Asus forced PAT and a latency change on the chipset to make the boards look good for reviews. I have a feeling the 1333 strap is forced at 400fsb but the latency we see at 1067 strap is still in play maybe...so it may be worth setting 400fsb, boot to windows and clock higher with clockgen for benchmark runs with this board
To finish...if you are clocking 1:1 I seriously suggest you skip 360 to 400fsb and push up from 401, the errors you see are NB related and not the memory in most cases.
That is it for the first installment...stay tuned for more.