RAM Dividers

[aj6065]

Could someone please describe to me RAM dividers for both the AM2 and Core 2 Duo platforms? I've been reading around for a while but just can't seem to completely understand it. For instance, if I have a 2:3 divider on the Core 2 Duo platform, or a 5:6 on the AM2, what does that really mean? Which number represents the RAM in the ratio, and which number respresents the FSB? And do you divide the first number by the second (2/3, or 5/6), or the second number by the first (3/2, or 6/5) (it seems every post I read is different)? And how do you apply this when overclocking to find out the different RAM speeds you can run at? Thanks a lot!

 

[ikjadoon]

RAM dividers, probably one of the harder concepts of overclocking.

For AMDs:

As you know, we overclock by raising the HTT(FSB for Intels). The memory speed, which is halved (DDR2-800Mhz runs at 400Mhz), must equal the HTT. So pretend we have a good 'ole X2 3800+. This has a clock speed of 2.0Ghz. The HTT is always set at 200Mhz for stock on all recent AMD processors. 200Mhz is stock for all of 'em. So 200 times what equals 2000(2.0Ghz)? 10, of course, which is our mutiplier. So we have 10x as multiper and 200Mhz as our stock speed. Say we are going to use DDR2-800 with this, whose clock is 400Mhz. The computer realizes this and puts on a memory divider which says run the FSB😀RAM (always in this order) at a ratio of 1:2. Meaning for every 1Mhz in the FSB, there are 2Mhz for the Memory. Get it? That way we can tell the computer to run a ratio to keep the components at stock, but it works the same for overclocking, continued below.

Pretend we want to push our processor more, but we have extremely sh!tty RAM which won't do a clock over 800. There are certain ratios that the motherboard knows. So we go into our BIOS and select DDR2-667 as the memory speed, which is in effect underclocking the memory. But when we OC and raise the HTT, the CPU's Ghz will go up and so will the memories, but it will rise from 667Mhz. It will go up from 667Mhz, not 800Mhz. Confusing, I know. Tell me if you still don't get.

This guide might help:

PCSTATS

~Ibrahim~

 

[aj6065]

That clears up a lot of things. Thanks. I just have a few questions to ask to make sure I really do understand it.

So basically, when you have a divider of x:y, and you say

The memory speed, which is halved (DDR2-800Mhz runs at 400Mhz), must equal the HTT.

you basically mean that ("x" divided by "y"), and multiplied by your RAM's actual clock speed, must be equal to your HTT (which has a stock of 200)? For example, I have my HTT at 200, my RAM is DDR2 667 (which is 333mhz), and my divider is 3:5. Then 3/5, multiplied by 333 = 200? (Can it be anymore confusing! 8O) Is this same concept also true for Intel platforms, namely Core 2 Duo?

If I was running a 1:1 ratio in the 3800+ example you had, wouldn't that result in running DDR2 400 RAM (clock of 200mhz), if all settings were left at stock, since the HTT is 200mhz?

If I had a 4200+ this time (multiplier of 11, I believe) and I was running DDR2 667 RAM, with all stock settings, it would look like this... HTT is 200, multiplier of 11, and the ratio would be 3:5?

Does all of this apply to Intel platforms, besides them using a FSB instead of HTT?

Again, thanks a lot ikjadoon

 

[ikjadoon]

Yeah, this is probably *the* most confusing part of overclocking, these accursed dividers.

Let me explain your example there. So we have a computer at stock, some DDR2-667, and a divider of 3:5.

3/5=.6

200/333=.6

See? 200 is the stock HTT and 333 is the stock memory. What ratio will equal that? 3:5 which is 3/5, but it looks cooler to say 3:5. 3 to 5. For every three clocks in the HTT, we have 5 clocks for the memory. This way we don't under nor overclock anything.

Exactly right! By God, I think he has got it! Yup. 100% correct, stock HTT is 200MHz, stock memory is 200Mhz, 1:1 ratio. If you have a 1:1 ratio, that means you don't have a ratio at all, but that is just politcally correct to say 1:1.

Right again with the 4200+ example!

Now there is one more thing I need to mention before I begin the talk on Intels. This article snippet from Hardware Secrets should sum it up:

The memory controller integrated on AM2 CPUs can support DDR2-533, DDR2-667 and DDR2-800 memories. The problem, however, is how the memory bus clock is achieved. Instead of being generated thru the CPU base clock (HTT clock, which is of 200 MHz), it divides the CPU internal clock. The value of this divider is half the value of the CPU multiplier.

For example, an AMD64 CPU with a clock multiplier of 12x will have a memory bus divider of 6. So this CPU will work at 2.4 GHz (200 MHz x 12) and its memories will work at 400 MHz (DDR2-800, 2,400 MHz / 6). Keep in mind that DDR and DDR2 memories are rated with double their real clock rate.

The problem is when the CPU clock multiplier is an odd number. For an AM2 CPU with a clock multiplier of 13x, theoretically its memory bus divider would be of 6.5. Since the AMD64 memory bus doesn’t work with “broken” dividers, it is rounded up to the next higher number, seven in this case. So while this CPU will work at 2.6 GHz (200 MHz x 13), its memory bus will work at 371 MHz (742 MHz DDR) and not at 400 MHz (800 MHz DDR), making the CPU to not achieve the maximum bandwidth the DDR2 memory can provide.

The specific processor they are talking about, the one with the 13x mulitplier is the X2 5000+, btw. This problem rarely happens, but it comes up and I thought I'd throw it in there.

For Intels, it is basically the same, but I'm not an expert with Intels. Just know that the FSB is quad-pumped, meaning it is mulitplied four times. For example, the Core 2 Duo machines use a FSB of 1066, which is actually 266Mhz. (1066/4=266) 266Mhz multiplied by the multiplier. Get it?

You're welcome!

~Ibrahim~

 

[aj6065]

Wow, it all seems so simple now :lol: . I can't wait until I build my new PC and start overclocking, now that I know what I'm doing. Thank you very much, again!

 

[ikjadoon]

Excellent. Remember: Good cooling, watch your temps, and bench like there is no tommorow! Good luck!

~Ibrahim~

 

[ChefOfDeath]

Sorry for bumping an old thread, but my question is along these same lines.

I'm planning to try to OC my e6600 to around 3 ghz, and Im using DDR800 RAM. To get the e6600 to 3 ghz, i need my FSB at around 333 mhz. If I keep my RAM at 400 mhz, will my divider be 5:6 (5/6=.833, x 400=333)? And would doing that be preferable to, say, throttling back to DDR 667 and running on a 1:1 divider?

 

[sunangel]

Why would you want to use a divider if you can get a 1:1? One thing I have noticed in all this discussion is the abscense of the JEDEC standard. If your multiplier doesn't divide the memory at the next JEDEC standard it gets pushed back to the previous JEDEC standard. So, if you have DDR2-800 and your FSB can not hit 400MHz you automtically get pushed back to DDR2-667. Thus, it makes no sense to purchase DDR2-800 or higher unless you going to do insane overclocking (maybe water, but definitely peltier or phase-change). All a divder does is increase the overhead on the NB.

 

[ikjadoon]

It is fine. In this case, it is better to bump an old thread than create a new one.

So, we have 9x as our multiplier, FSB 266. The Ratio seems right, 333/400=5/6.

What kind of RAM do you have? If it is known to OC OK-to-great, then just leave it on 5:6. If it is RAM that does not OC, bring it back down 667Mhz and a 1:1 ratio.

Of course, the first solution would be a faster overall speed, but it all depends on whether the memory overclocks.

Good luck!

~Ibrahim~

 

[ikjadoon]

Double post.

 

[ChefOfDeath]

It's corsair XMS2, from the reviews i've read it's supposed to OC fairly well. Stock timings are 5-5-5-12, although my mobo detected it at 5-5-5-18 and I haven't bothered to set it lower yet.

What kind of RAM do you have? If it is known to OC OK-to-great, then just leave it on 5:6. If it is RAM that does not OC, bring it back down 667Mhz and a 1:1 ratio.

Of course, the first solution would be a faster overall speed, but it all depends on whether the memory overclocks.

So if I can get it up to 333 without lowering the speed of the RAM, that would be better than lowering it in favor of a 1:1 ratio?

 

[tool_462]

Corsair XMS2 overclocks well. You should be able to keep it at 5:6, just make sure you set the voltage to whatever the specs on the RAM state. You can find your exact RAM and look at the voltage here.

One thing to look into is running a few benchmarks (SiSoft Sandra has lots of great memory benches) and seeing the difference in performance between the 1:1 @667 or the 5:6 @800.

Oh, and awesome job ikjadoon! 😀 Very well written and easy to comprehend. Nice to have members like you (that will answer any question without flaming someone for being "noobish") patrolling the forums.

 

[ikjadoon]

I don't get exactly what you are trying to say, but you mean that it would be better to get the FSB to 333Mhz w/o lowering the speed of the RAM, etc...?

Well, if you don't lower the speed of the RAM you'll be keeping a 1:1 ratio at all times..

~Ibrahim~

 

[tdng85]

first off, hi everyone! i'm new to this forum..

hm, so let me get this. So theoretically, for X2 4000+ can you just simply set fsb 266mhz x 10 = 2.66ghz, and buy ddr2 533, also sync with 266mhz, achieving 1:1..basically, there's really no need to buy ddr2 667 or ddr2 800 ??

 

[nawaz2kx]

Hi all,
I am a basic overclocker but not sure about ram dividers. I can't seem to get the best ratio for my X2 4600, I have 667mhz dual channel ram and I have a ratio of something like 5:6. I heard that having a 1:1 ratio increases the overclocking potential, is this correct? The cpu htt is at stock speed 200mhz.