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post #11 of 21
here ya go-> keep your ram at 200 or 1:1. you will see one of them in your bios. if you have trouble with POST, then get into bios and lower that **** to 166 or 5:6. also, if the computer does POST but you are not stable then lower the divider to the next one. try not to lower less than 166 or 5:6.

purpose of dividers is to keep computer stable when overclocking and/or get your computer to boot. raise the timing on your ram before using dividers to see if that works.
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post #12 of 21
Thread Starter 
Quote:
Originally Posted by Chozart
I'll give it a shot. You know the CPU has an external frequency of 200MHz, and runs on a mulplier on top of that frequency (your 3700+ has a multi of 11, thus running at 2.2GHz). DDR RAM works the same in a way, and DDR 400 runs on an external frequency or also 200MHz. With everything at stock values, the ratio between RAM external frequency and CPU external frequency is 200:200 or 1:1, which we call the 1:1 divider. Now, I guess you knew all this.

When you overclock, you will increase the external frequency of the CPU. However, despite the fact that you set your RAM at, for example, DDR 400 speeds (or 200MHz external RAM frequency), your effective RAM still will go up when you increase the external frequency of the CPU! In this specific case, it will go up with the CPU on a 1:1 ratio. Thus, when you overclock your CPU 10%, the CPU external frequency will be 220MHz, the CPU clock speed will be 2.42GHz (11x220), and the external RAM speed 220MHz, thus resulting in DDR 440 speeds. (remember, we're now still on a 1:1 divider).

Now, obviously, RAM can take only so much, and often less than the CPU. Let's assume that 10% is the max for the RAM. The 1:1 divider would then limit the CPU clock to 2.42GHz. You want to get higher though! Thus, time for a divider. You set the divider my adjusting the RAM frequency in the BIOS. For example, we want to get a bit higher, we set the RAM frequency at DDR 333, or 167MHz external frequency (whichever option your board offers). Now, at stock, external RAM frequency is 167MHz, and the external CPU frequency is 200MHz, or a ratio of 167:200, thus a 5:6 divider.

Now, lets increase the CPU external frequency to 240MHz, hitting a CPU clock speed of 2.64GHz (11x240). RAM frequency will increase together with the CPU frequency, but since we now set a divider of 5:6, we will get the following outcome: External RAM Frequency = 240/200 x 167 = 200MHz, or DDR 400 speeds. Hey, RAM is back at stock speeds, with a good overclock on the CPU! I hope you understand the logic behind this now.

Now, some motherboards allow you simply to set the RAM frequency higher than the CPU frequency, but this is not really a helpful function. First, you'll need DDR 500 or so RAM to do this, adn second, there is not a noticable increase in performance when you simply increase RAM speed (it won't be able to handle more than the CPU delivers anyways).

Now, what you should try is to find the Max CPU speed (knock RAM down on a heavy divider, and crank the rig up as far you can), the Max RAM speed (lower the multi, and keep going on 1:1 until the RAM does not want anymore), and the Max HTT of yuor motherboard (lower both RAM frequency and multi and clock the crap out of it). Now, when you know those values, you can try to find your ideal overclock. Let's assume your CPU maxes out at 2.8GHz and the RAM at DDR 440 or so, while the FSB can take a beating higher than those values (thus excluding it as a limiting factor).

For your CPU to hit 2.8GHz on a multi of 11, the external frquency has to be 2800/11 = 255MHz. On a 1:1 divider, this would result in a RAM speed of DDR 510, exceeding the RAM limit. Thus, we need to set a divider. The highest external frequency the RAM will do is 220MHz, while the CPU external frequency is 255MHz. This is a 220:255 or 44:51 ratio. Ideally, we want to set RAM on this divider, but your board will not give this option. At stock, the desired RAM speed to set for this divider is 400/51*44 = 345MHz. Then we look for the next lower available setting, which is DDR 333 speed! Thus a divider of 5:6 will work in this case.
Wow! Thanks, for the IDEAL information
And all you other guys (especially youroboros1827) thanks!
I understand it now. I got confused becouse I had read that 250 mhz ( RAM-FSB) was good. But many thanks!
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post #13 of 21
Thread Starter 
Quote:
Originally Posted by AMD-rules
Wow! Thanks, for the IDEAL information
And all you other guys (especially youroboros1827) thanks!
I understand it now. I got confused becouse I had read that 250 mhz ( RAM-FSB) was good. But many thanks!
EDIT:

I still don't get how you can let your RAM be faster than CPU. Is that like: RAM mhz is higher than FSB? Or should we start calculating on thins one

(Sorry Accidentle double-post)
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post #14 of 21
In this case, this will only work when you use RAM faster than DDR400. The reason why many people use DDR500 is because it will allow them to overclock higher on a 1:1 divider. I had DDR500 RAM that was able to reach DDR580 speeds (external frequency = 290MHz). My CPU had a multiplier of 10, meaning that I could reach 2.9GHz (10x290MHz) on a 1:1 divider, something that would never have been possible with DDR400 RAM.

Also, my motherboard at that time allowed me to set the RAM at 500MHz in the BIOS (external frequency = 250MHz.) If I would do that, the CPU would run at 200MHz (external) and the RAM at 250MHz (external) at stock. This is a 5:4 divider (RAM:CPU). However, there is no good reason to do this, since it will not result in a performance increase, or a marginal one at best. (RAM cannot handle instructions faster than CPU delivers them)
    
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post #15 of 21
Quote:
Originally Posted by ouroboros1827
The ideal ram speed is 200, but the ram can only run at a number that divides 2620 evenly. The computer will run your ram at the fastest number that goes into 2620 without breaking the 200mhz limit. SO, the computer will look at 2620/11=240, nope not low enough. 2620/12=218, nope not low enough. 2620/13=201, not low enough. 2620/14=187MHz. Lower than 200. Therefore, your ram would be running at 187MHz, not 200MHz. Again, why? Because the ram ALWAYS, always runs at a divider of the cpu speed. 200 does not divide into 2620 evenly, but 187 does.
Close, but not quite right.

The formula for calculating memory speed on A64 processors is:
(multi x fsb) / (multi x 200/divider) Rounded up to whole number = Memory Speed
(11 x 250) / (11 x 200/166) Rounded = Mem speed
(2750) / (13.25) Rounded
2750 / 14 = 196.42mhz (not 208.33, as you would have it be)

You can check this with CPU-Z and verify the bandwidths with Sandra.

You can download this. it shows both results, the "ceil" result is the correct one.
http://www.gurushane.com/site/software.aspx
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post #16 of 21
Quote:
Originally Posted by Chozart
In this case, this will only work when you use RAM faster than DDR400. The reason why many people use DDR500 is because it will allow them to overclock higher on a 1:1 divider. I had DDR500 RAM that was able to reach DDR580 speeds (external frequency = 290MHz). My CPU had a multiplier of 10, meaning that I could reach 2.9GHz (10x290MHz) on a 1:1 divider, something that would never have been possible with DDR400 RAM.

Also, my motherboard at that time allowed me to set the RAM at 500MHz in the BIOS (external frequency = 250MHz.) If I would do that, the CPU would run at 200MHz (external) and the RAM at 250MHz (external) at stock. This is a 5:4 divider (RAM:CPU). However, there is no good reason to do this, since it will not result in a performance increase, or a marginal one at best. (RAM cannot handle instructions faster than CPU delivers them)

I think my memory bandwidth is out of wack? Here are some of my screen shots. Can you tell me if it is wrong Chozart?

    
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post #17 of 21
LOL... looks like sisoft sandra is pulling a fast one on you.. That thing just went nuts on you I guess. The float looks reasonable though..

According to CPU-Z the RAM settings look ok. You're on a 5:6 divider I guess (ram at stock at DDR333 speeds), and the effective speed is knocked down to the nearest speed the RAM can handle, which is 275MHz (or DDR550 speeds, which is stock for your RAM). There is some rounding apparently (CPU-Z reports a couple MHz lower) but don't worry about that.

You seem to be running just fine. Only sisoft sandra is getting some hick ups. I would blame her more than I'd blame you
    
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post #18 of 21
Well it looked like under cpuz that the bus speed is 333 it should be 275 and the HT shows 1000 when it should be 825?
And I thought I was on a 1:1 not a 5:6?
I am Super PI and 3dmark stable, but not prime95?
    
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post #19 of 21
Those are your CPU settings... from what I gather, you have the following settings in your BIOS:

HTT = 333MHz (that's your bus speed)
Multi = 9 (resulting in a CPU Clock speed of 9x333 = 3GHz plus a bit of rounding)
HT Link = 3 (resulting in 1000MHz, plus some rounding)
RAM at DDR333 speeds (resulting in 275MHz, or DDR 550 speeds, plus rounding).

If these are settings in your BIOS, then everything looks fine. If Prime fails, maybe you need a little voltage somewhere (northbridge maybe?)
    
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post #20 of 21
Bump

Ok now??
    
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