e6400 overclocking question

ok so today my new parts came in, i got gigabye ga-965g-ds3 motherboard with an intel core 2 duo e6400 (using stock heatsink for it).

i also got some corsair XMS ram, two 512 sticks with timeings 5-5-5-15

anyway, i had a question about the guide on this froum:

Quote :

Part2. Memory Adjustments
**Expand options for Gigabyte BIOS under ‘M.I.T.’ by pressing CTRL+F1**
Gigabyte: Set ‘Memory Multiplier’ to 2 (1FSB:1RAM operation)
ASUS: Set ‘DRAM Frequency’ to DDR2-533 @266Mhz FSB (1FSB:1RAM operation)
As you increase the FSB, the RAM will follow in the pattern of 1:1 shown in BIOS.

1. Set ‘DRAM Timing’ to manual or disable SPD (use SPD for P5W DH)
2. In BIOS you will see 4 separate timing digits, change them to the ones specified on your RAM

When 1FSB:1RAM is overclocked above the rated frequency of your RAM use the following values
Timing: 5-5-5-15
vDIMM: 2.2V

e.g. DDR2-667 4-4-4-12 1.9V operating at ~400Mhz will need to be set to 5-5-5-15 2.2V

3. Leave the rest of other timings either at ‘Auto’ or at their default values

specificly i have a question about the bolded portions. when i set the memory multiplier to '2' it changes the ram freq to 533 (the ram is 800 though). should i take this up more so it says the freq is 800? or is it supposed to be lowered like that... if so, why?

i was also curious what the 1FSB:1RAM meant...

sorry if these seem like really retarded questions, im not all that great with computer hardware (software engineer in college lol), but thank you for any help you can give me anyway.

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FSB is the heartbeat of your system. Just about everything else's speed is derived from it.

CPU speed is FSB * [multiplier]. Since you have an E6400, your CPU speed is, with the default 266MHz FSB, 8*266=2130MHz.

Memory speed is 2 (the "double" in DDR=Double Data Rate) * Memory:FSB ratio (the 1:1) * FSB. The Core2 architecture apparently derives some performance benefit from running memory at 1:1 with the FSB. 266*2 *1:1=533MHz.

When you overclock a CPU with a locked multiplier, you raise your FSB. With DDR2-800 and decent cooling, you should be able to raise the FSB to 400 MHz easily enough. This would result in:

CPU = 8*400 = 3200MHz
RAM = 2*400*1:1 = 800MHz.

If you raise the FSB more, you may have to relax your timings to larger numbers than the specified 5-5-5-15 for your RAM. However, unless you have really good cooling (and/or are comfy with high temperatures), you probably won't be able to get too much further than 400MHz FSB anyway.

Reply to NotAPimecone

thanks a ton for your help, makes alot of sense now actually

so if i put the ram multiplier at say... 3... then i can take the FSB speed up till the ram is at 800 again? this would result in a lower FSB speed... and still higher than default processor speed?

Reply to Jimbo229

If you put the RAM multiplier at 3 (3:2 ratio), then the RAM will be at 800 for the default FSB speed of 266MHz:

2 * 266 * 3:2 = 798. This formula is the same as replacing the 2 from the double data rate with the multiplier: 3 * 266 = 798.

At 266MHz FSB, your CPU speed will be: 8 * 266 = 2128

In other words, you won't be overclocking at all. You will be running both your CPU and RAM at their specified speeds. Remember, CPU speed = FSB * CPU multiplier.

Reply to NotAPimecone

Quote :

In other words, you won't be overclocking at all. You will be running both your CPU and RAM at their specified speeds.

So, is there any advantage in performance in setting the RAM speed to the specified maximum (800)?

Reply to bleibert

Well, your RAM goes faster.

The C2D is supposed to be at its best when running in sync with the FSB. If you're not raising the FSB, 1:1 on a 266MHz FSB -> 533MHz RAM.
Supposedly, running RAM at 5:4 (667MHz on a 266MHz FSB) can actually hurt performance (relative to just running it 1:1), but running it 3:2 (800MHz on a 266MHz FSB) does increase performance.

I dug up a madshrimps benchmark that shows this phenomenon in action.

Reply to NotAPimecone

Quote :

I dug up a madshrimps benchmark that shows this phenomenon in action.

Thanks a lot, I understood it a bit more...
Since I am looking for a computer for Photoshop only, the 4% performance increase is not worth much to me. So even the cheapest and sub-optimal DDR2-400 CL5 will do.

I am planning a E6300 or E6400, and would like to have an OC option with a goal of 400 MHz FSB. Then a 400 MHz RAM would run with "half" speed, so I'd need 800 MHz RAM. Is then the increase in performance still supposed to be in the way-less-than-10% league, or will it be more significant with OC?

Reply to bleibert

I think you would not be able to overclock with DDR2-400, you'd have to underclock your FSB to 200MHz (unless your board has ratios less than 1:1), which would slow your processor down quite a bit. (1.4GHz for a E6300, 1.6GHz for a E6400).

In the madshrimps article, I believe, they did not OC anything. All they did was use different ratings of RAM and use RAM ratios to run them at their rated speed at the stock FSB of 266MHz. The performance boost was small becuase the RAM was the only thing running faster, and had to overcome the disadvantage of running asynchronously with the FSB (a problem that outweighed the advantages at 667MHz, or a 5:4 ratio to the 266MHz FSB).

If you OC the CPU, you should get a much more substantial boost in performance. A lot of boards don't even have ratios less than 1:1, so you'd pretty much be out of luck with DDR2-400, and DDR2-533 is not likely to cut it for overclocking either. According to wusy's guide: (the MHz numbers represent the FSB you can run the RAM 1:1 at)

Quote :

use RAM that’s rated:
-DDR2-667 4-4-4-xx (good for ~400Mhz*)
-DDR2-800 5-5-5-xx (good for ~410Mhz*)
-DDR2-800 4-4-4-xx (good for 500Mhz+*) ->Best for E6300/E6400
-DDR2-1066 5-5-5-xx (good for 530Mhz+*)

Reply to NotAPimecone

Quote :

I think you would not be able to overclock with DDR2-400, you'd have to underclock your FSB to 200MHz (unless your board has ratios less than 1:1), which would slow your processor down quite a bit. (1.4GHz for a E6300, 1.6GHz for a E6400).

Okay, I understand, what you are saying. But I have problems with the "reality". In the madschrimps article, he's running the system at the default 266 MHz FSB speed (I guess). If you want to run the RAM at 1:1 you need 2 x 266 MHz = 533 MHz RAM. But his benchmarks bases on a 400 MHz (5-5-5-15) setting. According to your statement above, he must have underlocked his FSB to 200 MHz or set the ratio to 3:4. I found some info on the used Intel Desktop mainboard D975XBX "bad axe" here, here and here. In the last link, there is a picture, which shows a BIOS setting:

System Bus Speed 1066 MHz
System Memory Speed 800 MHz

Is this the setting of the ratio? FSB clock rate is 266 MHz, data rate is 4 ("quad pumped" ) x 266 MHz = 1066 MHz, right? But what's about the memory? You explain:

2 (DDR) x (ratio x) FSB clock = memory speed

Mr. Madschrimps tells us:

2 (Dual Channel) x 2 (DDR) x FSB clock = memory speed.

Dual Channel - is this the thing with te two identical RAM modules installed? What was a standard almost 15 years ago in the Mac world?
So "your" memory speed would be 400 MHz, and "his" 200 MHz. Which is the right one?

And are there some typos here and here? At the first page there is at "Possible Memory Config(u)ration":

FSB1066 (266 MHz) DDR2-533 1:2.00

and at the second page:

FSB1066 (266 MHz) DDR2-533 1:1.00

?? I don't get it... :oops:
And at the second page, there is a column for FSB800 (200 MHz) - so you can set the FSB to 200 MHz (=downlock)? And there is lacking a fourth column for the FSB800 ratios? The identical ratio for FSB1066 and FSB800 makes no sense - to mee at least.

Quote :

In the madshrimps article, I believe, they did not OC anything. All they did was use different ratings of RAM and use RAM ratios to run them at their rated speed at the stock FSB of 266MHz.

If it was so, he must have set the the memory speed to 400 in the beginning as the zero point of his benchmark, right? So he set the ratio indirectly to 1:0.75?

Quote :

A lot of boards don't even have ratios less than 1:1, so you'd pretty much be out of luck with DDR2-400, and DDR2-533 is not likely to cut it for overclocking either.

I am thinking about the Gigabyte GA 965G DS3 - I read, it has very good OC capabilities, and I like the on board graphicsand the nice price. I will check for the possible range of the ratios, thanks for the hint.

Quote :

According to wusy's guide: (the MHz numbers represent the FSB you can run the RAM 1:1 at)use RAM that’s rated:
-DDR2-667 4-4-4-xx (good for ~400Mhz*)
-DDR2-800 5-5-5-xx (good for ~410Mhz*)
-DDR2-800 4-4-4-xx (good for 500Mhz+*) ->Best for E6300/E6400
-DDR2-1066 5-5-5-xx (good for 530Mhz+*)

Hm...
DDR2-800 @ FSB 500 MHz means a clock speed for the memory of 400 MHz, right? But this is no 1:1 ratio to the FSB rather a 4:5 (1:0.8 ) ratio - or am I just too stupid for all that stuff?

What is of interest for me is, what happens, if I set the ratio to 1:1, the FSB to 400 MHz, and have an "incompatible" RAM like DDR2-667 installed? Won't it boot? Will it be unstable? Or will it just run not "round" (slower)?

Reply to bleibert

I don't know much about the BadAxe, unfortunately. But I have to assume it has flexible enough ratios to allow 400MHz memory at 266MHz bus speed. This would not be too surprising, as the 975 chipset is a high-end enthusiast product. Just a lot ofmobos, as far as I know, don't have ratios below 1:1.

As for your questions about dual-channel, I'll explain as best I can, and I'll probably get some wrong because I don't know that much about it.

Anyway, we have to be careful with terms like "speed". I don't think dual-channel changes the frequency, it just doubles the amount of data that is transferred every cycle. One channel of memory is 64 bits (8 bytes) wide, so the theoretical peak bandwidth is:

8 (bytes) * FSB (transfers per second in MHz) * ratio (Memory:FSB) * 2 (DDR) * NumberOfChannels

Real-world analogy: Say you have sacks of potatoes to move from a storehouse onto a truck, and you have one worker to do it. The truck can take the sacks away twice as fast as the worker is loading them up, so you want the sacks loaded twice as fast. There are 2 ways:

(1) The worker must work twice as fast.
This is like increasing memory frequency - the worker will transfer sacks more frequently. But the worker can only work just so fast, just as memory can only work at just so high a frequency.

(2) You can hire a second worker, and split the potatoes up into 2 piles, 1 for each worker.
This is like dual-channel - now the CPU is getting memory twice as fast because it's getting data from 2 sources, each at the same speed.

I guess when they designed dual-channel, they wanted a way to increase performance without increasing memory frequency, because high frequency and low latency can be difficult to achieve. Obviously, dual-channel incurs a cost in a more complex memory controller, but it must have been easier to do than improving the actual memory itself.

This PDF gives some info on dual-channel.

Reply to NotAPimecone

This is a good topic for me since this is the one place I get a bit confused in O/C. I have a E6400 currently clocked at 333 Mhz (2.67Ghz) because I have DDR2-667 4-4-4-12 RAM so my understanding it that this is 1:1. I get a bit confused by things that say this is good to 400.

But according to wusy's guide if I want to go above this I have to go to 5-5-5-12 and 2.2V which is a big jump it seems to me. The timing changes I can kind of understand but the voltage change is substantial and I wonder why it needs to be so much (0.3V on a nominal 1.8V part is a 17% voltage boost and probably takes the memory to the top of it's datasheet operation).

Reply to DiverDave

I saw this in another thread about RAM timings: http://forumz.tomshardware.com/har [...] 81#1249881

Quote :

it's very difficult to find 1GB DIMMs that will run at DDR2-800 at the standard 1.8V. However, manufacturers can now produce plenty of DIMMs that will run at DDR2-800 at a slightly higher voltage, say 2.0V. (Remember, 6 months ago, it was hard to find DIMMs that would run at DDR2-800 under *any* voltage -- this is life on the bleeding edge.)
Thus, they may sell the DIMMs as "DDR2-800" memory

I would imagine this applies the same to overclocking 667MHz RAM to 800MHz.

Reply to NotAPimecone

According to Corsair's website the RAM is JEDEC tested at 675MHZ, 1.9V, 4-4-4-12 timings.

6 months ago when the first material comes out it's not surprising that it is hard to find something that works across the spec. But as time goes on they will likely improve their process and spec window as they prepare to move to the next technology node. So I'm wondering if the settings of 5-5-5-12,2.2V is still necessary for newer material.

I guess I can try it and if it dies I'll know

Reply to DiverDave

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