DDR2 Memory Speeds Explained - Page 2 - Overclock.net

Notorious · 02-15-08

Quote:

Originally Posted by durch

The purpose is to help people better understand how memory speed is calculated. What you do with the information is up to you, but it should help you get a better overclock

My main motivation was that a lot of people still say things like "set the divider" which was an option in the BIOS in the socket 939 and DDR days, but no longer has the same meaning with socket AM2 and DDR2 memory.

Take another look at rule #2, in bold it says "at the stock HTT of 200MHz". The memory's speed cannot exceed 400MHz for DDR2 800 when the HTT is 200MHz, however if you increase the HTT beyond 200MHz you can increase the speed of the memory beyond 400MHz. It can get confusing I know.

The divider is determined by following rules 1-3 described in my original post. Remember, these rules are used to calculate the memory's speed when the HTT is 200MHz, I think that's the part you're struggling with.

Taking your example of DDR2 667, consider this. At a CPU multiplier of 10x, and the HTT at 200MHz, the total CPU speed is 2000MHz. A divider of 5 gives 400MHz, which violates rule #2 (memory can't run faster than 333MHz at DDR2 667 and an HTT of 200MHz). A divider of 6 gives 333MHz, all rules are satisfied. I divider of 7 gives 286MHz, rules 1 and 2 are satisfied but rule 3 is violated because a divider of 6 works just as well.

If you increase the CPU multiplier to 11x (and hold the HTT at 200MHz), the total CPU speed increases to 2200MHz. Now a divider of 6 gives 367MHz, rule #2 is now violated. The computer knows this and increases the divider to 7, giving 314MHz, satisfying all rules.

It can be complicated I know, but if you understand the 3 rules you should be able to figure out what the divider will be for any combination of CPU multiplier and memory setting without using the charts. But until then, the charts can be a great quick reference.

I sense a lot of answers in your reply, but i have to read it more than 1 times haha, ok hmm so basically the divider for 667, 800 etc., are determine by what my CPU Speed are?

Example:
DDR2 800, Multiplier 16x, HTT 200MHz
divider 5 = 640MHz (violation)
divider 6 = 533MHz (violation)
divider 7 = 457MHz (violation)
divider 8 = 400MHz (satisfied)

So that means the divider is 8 for DDR2 800, Multiplier 16x, HTT 200MHz. (right?)

If memory cannot exceed 400MHz at HTT 200MHz for DDR2 800
What MHz the memory cannot exceed IF the HTT is 210 for DDR2 800

If memory cannot exceed 333MHz at HTT 200MHz for DDR2 667
What MHz the memory cannot exceed IF the HTT is 210 for DDR2 667

Thanks a lot! I understand more

durch · 02-15-08

Quote:

Originally Posted by Notorious

so basically the divider for 667, 800 etc., are determine by what my CPU Speed are?

Not exactly. The variables in determining the divider are a) CPU multiplier and b) memory setting (i.e. DDR2 800, DDR2 667, etc). So for any given memory setting, the only other thing you need to know is the CPU multiplier. Total CPU speed depends on the CPU multiplier AND the HTT, but your divider stays the same no matter what HTT you use. The divider only depends on the memory setting and CPU multiplier.

Quote:

Originally Posted by Notorious

Example:
DDR2 800, Multiplier 16x, HTT 200MHz
divider 5 = 640MHz (violation)
divider 6 = 533MHz (violation)
divider 7 = 457MHz (violation)
divider 8 = 400MHz (satisfied)

So that means the divider is 8 for DDR2 800, Multiplier 16x, HTT 200MHz. (right?)

If memory cannot exceed 400MHz at HTT 200MHz for DDR2 800
What MHz the memory cannot exceed IF the HTT is 210 for DDR2 800

If memory cannot exceed 333MHz at HTT 200MHz for DDR2 667
What MHz the memory cannot exceed IF the HTT is 210 for DDR2 667

Thanks a lot! I understand more

There you go, you're getting it! As the HTT is increased, the divider will stay the same. So the memory will start to overclock as you increase the HTT.

You can think of it like this:
Memory is rated to run at certain speeds, timings, and voltages at a stock HTT of 200MHz. For DDR2 800, that speed is 400MHz. The manufacturers make no guarantee that the memory will work at faster speeds, so the computer is setup to choose a divider that won't allow the speed to exceed 400MHz in a traditional non-overclocked system with the HTT equal to 200MHz. That's why when figuring out the divider you assume the HTT is 200MHz. But once the divider is chosen, it stays the same unless you change the memory setting or CPU multiplier. So as the HTT increases, so does the memory's speed. You can take it well beyond 400MHz if you have good memory.

Notorious · 02-15-08

Cool! So how much will the memory get increase if i increase HTT to 210, if HTT 200 results in 400MHz for memory?

How much can we push the memory? I'm using Corsair TWIN2X2048x6400 kit, how far to increase that the result will be safe and sweet.

By the way, since i don't know how to overclock the professional way, i only know how to do it by adjusting the multiplier like everyone said especially Tom's Hardware, so i wanna learn to use the multiplier and HTT to overclock so that i can overclock the memory as well.

I can't increase the HTT somehow, i've tried few times, there was one time only a mere 210 and leaving the multiplier on it's default 13x, the PC won't boot up, did i miss something? I noticed cool and quiet is disabled, what else should i check for?

Thanks durch

durch · 02-15-08

Ok, so the first thing you do is figure out what divider you're using based on the two factors a) CPU multiplier and b) memory setting. Once you know the divider (and know that the divider won't change unless you change the memory setting or CPU multiplier), then you can calculate the memory's speed using the equation in my original post:

memory speed = (total CPU speed)/divider

So as the HTT is increased to overclock the CPU, the memory will also start to overclock.

You asked how far you can push your memory, and that's something you can only find out through experimentation. If the memory becomes unstable, the first thing you should do is loosen the timings from 4-4-4-12 to 5-5-5-15. You'll probably need to do this somewhere between 425MHz (850 effective) and 475MHz (950 effective), but that's just an estimate, no way to know for sure where your RAM will become unstable. If you hit instability with 5-5-5-15 timings, then consider giving your memory a bump in voltage, nothing more than 0.1 volts though to be safe. After that, your options are pretty limited.

I'm working on an overclocking guide for AM2/DDR2 systems, I'll let you know when I've completed it. But until then, there's some overclocking guides here for socket 939 systems that might be of some help (although they use DDR memory so many of the steps aren't relevant to DDR2 and socket AM2). Check out the stickies in the AMD General section. You can also browse google for some good guides. Goodluck!

Notorious · 02-17-08

Oh thanks, i think that guide will help me understand more, but you've did a good job so far, i think i finally understand, i just need to get my hands dirty and experience it.

So far i did some simple test

I tried Multiplier 13x (default) and HTT 200MHz (default) = 2600MHz
Divider for DDR2 800 is 7 (371) so divider will stay the same (7) heh

So now i increase the HTT to 230MHz, 13x230=2990MHz
2990/7=427MHz

I used CPU-Z and checked the memory and got 427.3MHz

This....means.....i'm successful eh?

The hard part is to overclock to the CPU speed i want sometimes i can't get the RAM speed i want, it maybe too much or too little.

To use multiplier 12x for example, to get the desired speed of 3000MHz, i increase HTT to 250MHz and since divider is 6, the results is 500MHz, that's a bit too much for me i think :x

I guess multiplier 10 and 12 are got memories above DDR2 800, so far i find 13x has some sweet spots, like 13x240MHz = RAM 445MHz, 13x250MHz = RAM 465MHz.

But i think i will try 13x240, since my MOBO won't allow me to increase CPU voltage over 1.350V so i can't go above 3100MHz i think.

Thanks. Lookin forward to the AM2/DDR2 guide from you.

adramalech707 · 03-14-08

okay i am having such a delema trying to figure out an over clock...i have been racking my brain over how to write an equation of the two different things...the memory divide that cannot exceed a max speed and the correct divide value dependent on the divide and dependent on the cpu multiple...whooowwww i hope i didn't try and confuse anybody...

okay i have a x2 4600+ @200x12(2400mhz) 1.35volts....

i also have 4gb 2x twin2x2048-6400c4...which is proving very difficult to overclock my cpu with 4 stick population!!!!

on a ga-m59sli-s5 (which has problems going above 312mhz fsb!!!

)

i have tried numerous different approaches to ocing this chip on this board in order to not get the newer meaning of 1:1 ratio which i have found to me is unreachable!!!!

i am know trying to get 3.2ghz just because i think it would be cool and because my motherboard i think can handle the overclock...but the memory is as i stated earlier a pain in the arsseee to keep undercontrol and stable in an overclock...

the reason why i am trying for 3.2ghz is because at the time i was thinking to keep memory under 800mhz (or 400) but i forgot that to divide by 8 i would have to lower divide to 533 which would only allow for 267mhz and then i would have to rethink the whole idea...

can someone please enlighten me on an easier approach than what i am trying

because i cannot seem to keep the speed of the processor under the limit of the memory...if i am wrong please tell me so i don't go around thinking the impossible with this oc

slowpoke2006 · 05-26-08

OK i have just one question If you have DDR2 667 and you now it will run over 800 can you just set it to DDR2 800 in the bios? so far i know it runs stable at 800 just haven't tried to go any higher yet. Edit ok i passed the 900 mark on my mem. running 5-5-5-15-20 2T at 2.0v. and i can keep going but i have just one problem I guess i ended up with a bad board b/c my HTT clock wont go over 280 don't know why, but in Ntune i got it to go all the way up to 340. Ive tried to drop the HT Multy down to 4 but steal no good. So i sad what the heck now I'm running at DDR2 800 speeds with a Htt set at 200.9 so now i can push my ram even farther maybe even get to 1000 at 2.1v who knows it seams to be a really good batch of memory. My HT will run stable at 1400mhz after that it down for the count.

karossii · 06-02-08

I want a cookie

- my MSI K9A2 CF mobo has a CPU:memory ratio option in the BIOS (AMI BIOS A7388AMS rev 1.6).

It is AM2 and uses DDR2.

Which is why this and other posts have been confusing me with all the talk about dividers with options I can't seem to access. Where do I learn more about overclocking with this seemingly archaic usage?

durch · 06-09-08

Quote:

Originally Posted by slowpoke2006

OK i have just one question If you have DDR2 667 and you now it will run over 800 can you just set it to DDR2 800 in the bios? so far i know it runs stable at 800 just haven't tried to go any higher yet. Edit ok i passed the 900 mark on my mem. running 5-5-5-15-20 2T at 2.0v. and i can keep going but i have just one problem I guess i ended up with a bad board b/c my HTT clock wont go over 280 don't know why, but in Ntune i got it to go all the way up to 340. Ive tried to drop the HT Multy down to 4 but steal no good. So i sad what the heck now I'm running at DDR2 800 speeds with a Htt set at 200.9 so now i can push my ram even farther maybe even get to 1000 at 2.1v who knows it seams to be a really good batch of memory. My HT will run stable at 1400mhz after that it down for the count.

You know this is a question I've had for awhile too but never bought DDR2 667 to experiment with. It sounds like you were able to set the DDR2 667 to DDR2 800 in the BIOS without overclocking the reference clock (HTT), is this correct? I'm definitely interested in knowing.

As for your reference clock (HTT) not going over 280, try giving the motherboard voltage a few bumps. Also, make sure it's not your CPU that's holding you back. When testing for the max reference clock (HTT) you want to make sure neither the CPU or memory goes over stock speeds.

Quote:

Originally Posted by karossii

I want a cookie

- my MSI K9A2 CF mobo has a CPU:memory ratio option in the BIOS (AMI BIOS A7388AMS rev 1.6).

It is AM2 and uses DDR2.

Which is why this and other posts have been confusing me with all the talk about dividers with options I can't seem to access. Where do I learn more about overclocking with this seemingly archaic usage?

<-- starts baking

But you cheated, you're using a 790 board that came out after I wrote this lol. I haven't used an AMD system in several months now, interesting to see that at least some boards are going back to the 939 days of ratio's. Because the divider depends on both that ratio and the CPU multiplier, the ratio you choose will only be correct if you're running an even CPU multiplier. It's going to make it a little hard to figure out what your memory speed actually is, but that's what CPU-Z is for. I'm not sure what ratios your board gives, but here's some general correlations for an even CPU multiplier and a stock (200MHz) reference clock:

1:1 DDR2 400
3:4 DDR2 533
3:5 DDR2 667
1:2 DDR2 800
2:5 DDR2 1000
3:8 DDR2 1066

Lightning_Scythe · 07-13-08

a friend of mine is running an X2 6000+ @ stock with 2 2GB DDR 2 800mhz sticks of ram.

based on ur article i wud believe that the divider would b 8, and thus have a memory speed of 3000/8 = 375 mhz per channel or 750 mhz. this is confirmed by the ddr2 ram divider charts which u linked us to.

however his frequency monitor (i believe he is using ntune) is saying that his frequeny is 804 mhz. what would cause this, considering he has done no overclocking?

he is using an asus m2n32-sli vista edition

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