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The definitive guide to Intel chipset/memory over clocking.
After many years of over clocking Intel based platforms and studying Intel chipset white papers I think its time to pass on some of the knowledge I have acquired.
Ever since Intel launched the 865 chipset over clocking the chipset has been a major factor in enhancing Intel motherboard performance. We all know that Intel force the CPC on their chipsets to 2T , a way to claw back some of the performance is to clock the chipset higher, which in theory reduces its internal latency and improves memory performance,
So how do we over clock the chipset?
Asus pretty much were the pioneers of this, they found the chipset register which enabled “Performance Acceleration technology” or “PAT” on the 875 chipset and went looking thru the white papers for the 865 chipset to see if any settings/registers had the same effect. What they found was that the 865 chipset forced to the 533 strap (133fsb for us mortals) set the same register as the 875 chipset with PAT enabled. They also found at lower strap values Intel forced a latency change on the chipset that improved memory performance with the memory being at a lower clock speed. Many will have seen this register as it was adjustable with the “875 tweaker” application that many used on the 875 and 865 boards.
Moving on we need to see how forcing a lower strap on the chipset actually over clocks it.
Think of the NB chipset as a CPU, it has an internal clock speed and a multiplier. If we use the 800 strap as a base and for the sake of this article say the NB has a clock speed of 400MHZ. The applied FSB to the actual CPU is 200fsb and the applied FSB to the NB is 100FSB with a multiplier of 4.
If we change the strap now to 533 the chipset FSB moves proportionally to the CPU FSB. So 200CPU FSB now moves to 133FSB and 100NB FSB moves to 67FSB. This drops the internal clock on the NB to 268MHZ with the 4 multi, so to compensate the chipset would alter its multiplier to 6 which again would put the internal clock at 400MHZ.
Now Asus forced a 533 strap on the 865 chipset at 200fsb CPU which would force the NB to run at 100MHZ FSB , if the NB applied a 6 multi at this speed its internal clock would be 600MHZ which is way above what it normally runs at. Many users did see that the NB with Turbo mode at 200fsb on the 865PE Asus motherboards get real hot…now you know why ;-)
The only down side of this was that you lost some memory ratio’s, what was a down clock at 800 strap mode suddenly could become 1:1 and upclock ratio’s may not have worked. You have to remember that memory ratios are set by the chipset strap. 1:1 in 533 strap is not 1:1 in 800 strap etc.
So moving onto the 975 chipset, what are the effects?
We all know Conroe sets 1066strap; this means it forces the board to boot at 267fsb. Now many boards are hitting a limit at 370fsb and stopping dead, we all know the CPU and ram can clock higher so what is causing the boards to become unstable…the answer is the chipset.
At 267fsb the chipset is at its normal working frequency, as you push the CPU FSB higher you are pushing the NB frequency higher, eventually just like a CPU it hits its limit. Now you have to remember that Intel seems to alter the internal latency on its chipsets dependant on strap also, this is why we see end user comparisons at the same clock speeds but different strap values showing different performance, lower strap equals improved performance at the same CPU and ram frequency.
Now we need to look at memory ratios.
In 800 strap we have the following ram ratios.
400,533,667,800 or as some quote them 1:1, 3:4, 3:5, 1:2
In 1066 strap we see the following.
400, 533, 667, 800 but the actual ratios have altered, 400 mode is now a down clock so the following applies.
400=4:3, 533=1:1, 667=4:5, 800=4:6
Moving to 1333 strap we see another change.
400= 5:3, 533=5:4, 667=1:1, 800=5:6
On some boards you may also see options for 889, 1066 etc, they apply these extra ram speeds thru chipset strap manipulation, there is no 3:4 or 4:5 available in 1333 strap mode but you can force this option if you change the NB strap to the lower value that applied them. I have also seen tweaks that apply the higher FSB to the NB but force the NB to use the lower multiplier so allowing the extra ram options to work well as the chipset is not massively over clocked. It all depends on how the board was designed and how good the bios is.
Now we have the question regarding why 1:1 in 1066 strap have better memory performance that 1:1 in 1333 strap? The answer is in the chipset its self. Lower strap means lower internal latency to compensate for the lower overall memory clock speed, so a higher strap will have a higher less efficient latency and so lose performance. There will be a way of setting the higher strap value but forcing the lower latency on the chipset. This would work well with the chipset near its base clock speed and show awesome performance gains, BUT….would greatly limit the over clock capabilities the chipset has.
To finish I will try and show you what the ultimate 975 board should have available thru bios.
To be able to clock Conroe well over 370 FSB we need to be able to force the 1333 strap on the CPU, this would set the clockgen back to a default option(333FSB base frequency) and allow it to again scale quite high. What we also need though is the ability to set the NB strap to any option we want also, independently to what the CPU strap is, this would allow us the option to over clock the NB its self. Finally the option to adjust the NB latency, like we had in “875 tweaker”
With all these tweaks you would be able to force all manner or ram ratios and latency tweaks and fine tune the system for ultimate benching…the only issue is it would push up the cost of the boards.
Next I will explain how this all effects memory overclocking etc.
Moving on its time I explained how we get the other ram ratio's you sometimes see on Abit, Asus and Gigabyte boards.
Using a conroe with a base FSB of 267 and base strap of 1067 we sometimes see the following options for ram speed in bios.
888, 1067, 709(712), 800, 667, 533, 400
As you will have seen from my previous post the main options per strap for the memory controller are 400, 533, 667 and 800 in all strap settings, although they all use different dividers to get the speeds; so how do we get the rest?....answer...manipulate the chipset strap!
If you look at the 800 strap, which you usually see if using an 800fsb CPU, you see it applies the following ratio's to attain the memory speeds at 200fsb:
1:1 for 400DDR
3:4 for 533DDR
3:5 for 667DDR
1:2 for 800DDR
Now, what happens if we apply a base FSB of 267 to these ratio's?
We get the following:
1:1 for 533
3:4 for 712
3:5 for 888
1:2 for 1067
1:1 would not normally***(see note below) be used as its easier to implement 1:1 from the 1067 strap "as per stock C2D strap" as its keeping the same strap for CPU, clockgen and NB which is the most compatible.
So moving on we ask the question how does this effect overclocking on the memory?
As I said before if you want to gain performance from an Intel chipset you overclock it...to do this you lower the strap..IE go from 1067 to 800 NB strap. As you see to attain these added ratio's the motherboards are infact altering the strap on the NB to overclock it and allow the added memory bus speeds....this can be good and bad. In short if you are using 888 1067 712 modes you need to remember to keep the CPU fsb low...as near to default as you can as the higher you push the least chance the NB has of running stable as its already overclocked.
To test ram you need to remain on one of the known 1067 strap ratios..IE 800 and 667 . ***Some manufacturers have implememted 800 strap to do 533 and 400 on the memory as this overclocks the NB and makes their boards look fast in reviews, the issue with this is it does not allow the CPU fsb to ramp high as the NB craps out way before the CPU does. This explains why some boards clock ok in 667 and 800 mode but not 533 and sometimes 400.
If you want to make sure your ram is ok test ONLY with 667 or 800 mode, this will limit the FSB the CPU may do but it will prove if the memory can do the speeds you are looking to push it to without the NB limiting you.
If you find you can not overclock at all well in 533(1:1) mode on your motherboard please try 667 or 800 and see how the CPU and ram overclocks, this will prove if the board is setting a lower strap for 1:1 mode to enhance its performance. Another way to help the NB in an overclocked state is to losen the memory timings, even though they are lose it may still end up being faster as the NB is running at a much faster speed on the lower strap ratio.
You may feel the ram will not do its rated speeds, this will probably NOT be the case...the issue will be the NB is overclocked and will not run the ram at the speeds you want it to.
So the saga continues...how to make a board ubber fast at stock speeds so reviews look awesome
Now you all seem to have a reasonable idea of how straps work i will show you how the motherboard manufacturers manipulate them in bios to make the boards work faster than the competition in reviews.
Using a conroe, which has 1066 strap and 267fsb we all know that 1:1 is 533 on the memory. Now if you want your board to work around 5% faster all you do is lower the strap but keep the ram ratio at 1:1.So you force the strap on the clockgenerator to 1066 but you trick the NB to run on the 800 strap in 400 mode.
On a 965 board this would allow 400fsb+ in theory on the CPU but there is no way the NB would run on the high 800strap internal multi and high bus speed without luck in you gettting awsome silicon and a ton of voltage.
At 267fsb on the CPU though the NB stands a good chance of working just fine, its moderately overclocked but not to stressed....and you gain 5% or so performance from the memory which transaltes into more FPS in game benches.
This is why when I ask you to test ram you need to do it with the 667 or 800 memory ratio, i already know 712,888 and 1067 are 800 strap, what i don't know is what 533 is latched too, as it could easy be off the 800 strap to improve performance at low clocks 1:1.
It seems many boards are setting memory timings covertly, some good work by OCZ customer Simonmaltby over on Xtremesystems uncovered some interesting info. http://www.xtremesystems.org/forums/...d.php?t=111400
Basically what he found was altering the timings in windows allowed him to overclock the memory higher. You will need the 975 tweaker available here