am2 ddr2 dividers

[breakfromyou]

This should be stickied...seriously. When i need to find it while at work, and the computer at work refuses to take my flash drive, this would be REALLY nice to have.

[JumpingJack]

This should be stickied...seriously. When i need to find it while at work, and the computer at work refuses to take my flash drive, this would be REALLY nice to have.

It is actually simple, you do not need a table.

Memory speed will be clocked by the divider as CPU clock / divider integer.

For example, a processor running DDR2-800 has a would ideally clock the memory 400 MHz (double date rate = 800 by nomenclature), so a 2.4 Ghz AMD AM2 CPU will use a divider of 6 to get 400 Mhz to time the clock

Mem speed = CPU/mem divider

The caveat is that Mem speed <= rated memory speed (i.e. less than or equal to rated speed), otherwise use the next highest divider integer.

For example, using my DDR-800 info above.

a) 2.4 GHz CPU, 2400 Mhz / 6 = 400 MHz for DDR2 -800 -- everything is ok here.

b) 2.5 GHz CPU, 2500 Mhz/ 6 = 417 Mhz for DDR2-800 <==THIS ONE WILL NOT WORK because it would time the memory above it's rated value. Therefore, use the next highest divider, 7.... thus a 2.5 GHz AM2 CPU will time DDR2-800 not as 400 Mhz but as 2500/7 = 357 Mhz or the nomenclature equivalent of DDR2-714

Jack

[Lufusol]

It is actually simple, you do not need a table.

Heh.. simple, he says.

I think the best thing about the table isn't the data in white, but that it tells you what the memory dividers are for a given CPU multi. Does your formula intend to predict what mem divider will be used at a given multi because I'm not seeing that.

I could use a table with half multis. On my GB 780g board with opty 1210 it shows half steps up to 8.5x (gigabyte needs to fix this. 1210 is 9x native!! ) - I really need to know what the memory dividers will be for half multis so I can test max stable CPU/mobo overclock without overclocking my memory at the same time.

edit: ok now I am seeing that So to figure out the memory dividers I have to ignore my target HTT and work with stock HTT for my CPU (200):

first take my stock htt (200) and multiply by my desired cpu multi = a very boring cpu speed, but I need this number.
example: I want to find the dividers used for the 8.5x multi. so 200 x 8.5 = 1700
then to find the memory dividers used for my target cpu multi (8.5x)

"DDR 400": cpumhz / 200 = some integer (ex. 1700 / 200 = 8.5...)
"DDR 533": cpumhz / 266 = some integer (ex. 1700 / 266 = 6.4...)
"DDR 667": cpumhz / 333 = some integer (ex. 1700 / 333 = 5.1...)
"DDR 800": cpumhz / 400 = some integer (ex. 1700 / 400 = 4.3...)

then take "some integer" (in my examples 8.5, 6.4, etc.) and round that number up to the nearest whole. that is your divider

so for 8.5x multi, which results in a cpu frequency of 1700mhz at the stock 200mhz htt, my dividers are:

"DDR 400" = /9
"DDR 533" = /7
"DDR 667" = /6
"DDR 800" = /5

gotcha, thanks!

[Lufusol]

Now that I know my dividers I can apply it to my overclock.

As a result of my finding the proper memory dividers, I settled on the 8.5x multi and HTT of 333, (2830.5mhz) and using the "DDR 533" setting which is a memory divider of 7. So 2830.5mhz/7=404.35mhz or effective rating of DDR-809 (rounding up a notch). Close enough!

I hope that example is useful to someone, though here on XS i suspect not so much.

By the way, with stock voltages, I booted into xp, but got reboots when loading cpuz, or even navigating folders. Upping just the BIOS cpu voltage from 1.250 (stock) to 1.275 resulted in a stable desktop, CPU-z reports 1.28-1.29 core volts at rest and instead of the vdroop i'm used to on intel boards, I see a rise to 1.344v under load (thank you gods of AMD motherboards?). Orthos stable for 2 hours 15 minutes, now. Amazing what a teeny tiny bump in voltage can do. Will try for 3.0ghz+ later....

[ramman949]

Hi Guys,

Im sorry, but Im confused. I have a oddball gigabyte motherboard. GA M571SLI-S4 with a AMD 4800+


My CPU has a multiplier of 12.5 and my motherboard doesnt allow me to choose a divider in a number form. Instead its listed as 400/533/667/800. Because of that, I have a hard time trying to figure out what my RAM speed will run at without trial and error or booting up windows and running CPUZ.

Im curious to know how I can figure out what the divider # would be if I use a odd multiplier so I can run the math before I try the settings.

For example, say I want to lower my stock multiplier of 12.5 to 11.5. How do I figure out what the divider is when I choose a memory speed (400/533/667/800)?


Thank you all and sorry if this has been covered. I just dont get it.









Can anyone help me?

[Particle]

Old thread, but what the heck. Your CPU uses a multiplier of 12, not 12.5. As such, just look at the 12x chart on the first page and look across the top for the RAM setting (400/533/667/800) and along the left for the HTT speed you're setting. The cell that crosses both will tell you your real RAM speed.

[ramman949]

Old thread, but what the heck. Your CPU uses a multiplier of 12, not 12.5. As such, just look at the 12x chart on the first page and look across the top for the RAM setting (400/533/667/800) and along the left for the HTT speed you're setting. The cell that crosses both will tell you your real RAM speed.

Thank you for the correction about my stock multiplier. For some reason I thought it was 12.5.

That said, say i want to drop my multiplier to 11.5 or 10.5, how do I figure out what the divider is per speed choices I have (400/533/667/800)?

I can do 12 X 250 @ 3.0ghz with memory @ 750mhz (667 memory ratio)

I can do 11 X 272 @ 2992mhz with memory @ 861 (667 memory ratio)

I can do 10 X 300 @ 3.0ghz with memory @ 750mhz (533 memory ratio)


As you can see, the 2nd option seems best since it gets my memory speeds up. But I would like to see what 11.5 and 10.5 can do. I just dont know what memory ratio to choose without it either being to low of a memory speed or it forces my CMOS to lock up and me having to clear my CMOS and do all my settings again.

[Particle]

It's pretty easy. You just have to figure out the divisors for a multiplier assuming an HTT of 200. For instance, let's look at 11.5.

First, figure the theoretical product of the baseline HTT and multiplier:
(200 HTT * 11.5x) = 2300MHz Clock

Next, figure out what that clock speed divided by the (real) RAM frequency is, and round up. Take note that DDR2 speeds are marketed as double what they really are. This makes 400 = 200, 533 = 267, 667 = 333, and 800 = 400.

So for the 400MHz setting, you'd do: (200 HTT * 11.5) / 200 = 11.5

Round up and you get 12. So, with an 11.5x multiplier and RAM set to 400 at an HTT of 200MHz, you'd have an actual memory frequency of 192 (384) MHz.

For the 667 setting at 11.5x and 207MHz HTT for example, you'd have:

Ceiling((200 * 11.5) / 333) = 7

(207 * 11.5) / 7 = 340 (680) MHz

[ramman949]

It's pretty easy. You just have to figure out the divisors for a multiplier assuming an HTT of 200. For instance, let's look at 11.5.

First, figure the theoretical product of the baseline HTT and multiplier:
(200 HTT * 11.5x) = 2300MHz Clock

Next, figure out what that clock speed divided by the (real) RAM frequency is, and round up. Take note that DDR2 speeds are marketed as double what they really are. This makes 400 = 200, 533 = 267, 667 = 333, and 800 = 400.

So for the 400MHz setting, you'd do: (200 HTT * 11.5) / 200 = 11.5

Round up and you get 12. So, with an 11.5x multiplier and RAM set to 400 at an HTT of 200MHz, you'd have an actual memory frequency of 192 (384) MHz.

For the 667 setting at 11.5x and 207MHz HTT for example, you'd have:

Ceiling((200 * 11.5) / 333) = 7

(207 * 11.5) / 7 = 340 (680) MHz

Thank you for spending the time to help me. I understand what you are saying until you get to the Round up part. I understand you have to round up, but what is the formula to get to 192 (384)?

Thanks again!!!

[ramman949]

...wait.

Let me try using 10.5 multiplier


200HTT X 10.5 = 2100

800mhz divider:
2100 / 400 = 5.25, round up = 6

667 divider:
2100 / 333 = 6.30, round up =7

533 divider:
2100 / 266 = 7.89, round up = 8

400 divider:
2100 / 200 = 10.5, round up = 11


Is that right?

[Particle]

Looks right, ramman. If you get a perfectly even number you keep it. Otherwise round up like you have been. The point there is that the system's divisor is always chosen on the safe side of the RAM's limit (at default HTT).

[cbjaust]

I'm pretty sure that the CPU just uses a look up table to select the right RAM ratio, but another way to look at is for each RAM frequency there is a corresponding RAM RATIO. So DDR800 as stated in the BIOS indicates a ratio of 1.0, DDR667 = 1.2, DDR533 = 1.5 and DDR400 = 2.
Now the RAM Divider can be derived from the CPU multiplier and the RAM ratio and the integer 2 for DDR2:
RAM divider = (CPU multi x RAM Ratio)/2 --> rounded up to the next highest integer.

It's the same thing but a bit easier as you are not concerned with what the HTT is.

Eg from the 667 divider example above: (10.5 x 1.2)/2 = 12.6/2 = 6.3 --> 7 so the MEM Freqency will be 2100/7 = 300MHz

Cheers

[ramman949]

^^^ oh I like your way! Makes it much easier. Thank you both.


Now Im off to figure out why my SPD memory timings dont match CPUZ. Bios has 4-4-4-15 and CPUz shows 4-4-4-18 on the memory tab.


Thanks again!

[Particle]

Avast, I've been outdone. How about this then?

http://downloads.pcrpg.org/comp/automemcalc.zip

(Requires .NET 2.0 framework or better.)

It will auto-calculate all HTTs between 150 and 350 for any full or half multiplier between 6.0x and 24.5x for you and for all RAM settings: 400, 533, 667, 800, and 1066.

Let me know if you like it.

[ramman949]

Old thread, but what the heck. Your CPU uses a multiplier of 12, not 12.5. As such, just look at the 12x chart on the first page and look across the top for the RAM setting (400/533/667/800) and along the left for the HTT speed you're setting. The cell that crosses both will tell you your real RAM speed.

Hey Particle,

Just thought I would share this with you. I noticed that if my system BIOS is set to default/auto, my CPU actually runs at 12.5. Not 12. I have also found a few links mentioning the 4800+ does have a 12.5 multiplier. But I also saw some that said 12. Perhaps AMD made a revision down the road?


On a side note, upon playing with my memory and CPU speeds, I had also noticed my BIOS and CPUZ were NOT matching on the memory timings. I contacted OCZ (brand of ram I have) and asked them why I was seeing a difference between CPZ and my BIOS, and they suggested I update my BIOS. I did that and that fixed my memory timings issue.

But... my CPU still defaults at 12.5 according to my BIOS and runs at 2500mhz.

Is that odd or what?

[ramman949]

Avast, I've been outdone. How about this then?

http://downloads.pcrpg.org/comp/automemcalc.zip

(Requires .NET 2.0 framework or better.)

It will auto-calculate all HTTs between 150 and 350 for any full or half multiplier between 6.0x and 24.5x for you and for all RAM settings: 400, 533, 667, 800, and 1066.

Let me know if you like it.

OMG... now this makes its REALLY easy! I like this a lot! Thank you VERY much!!! Thank all of you!


Now I need to run some tests to see what setting would be ideal.


12.5 X 240 @ 3ghz with memory set to 800mhz running @ 858mhz

12 X 250 @ 3ghz with memory set to 667 running @ 750mhz

11.5 X 262 @ 3ghz with memory set to 667 running @ 861mhz

11 X 274 @ 3ghz with memory set to 667 running @ 862mhz

10.5 X 286 @ 3ghz with memory set to 667 running @ 858mhz

10 X 300 @ 3ghz with memory set to 533 running @ 750mhz (this setting doesnt always play nice)


Looks like I have some benchmarking and stability testing to do.

[Particle]

Glad you like it. And yes, defaulting to 12.5 is very odd. The model you referenced is a 12.0x model, so it's odd that your board is upping it a half step.

[ramman949]

Glad you like it. And yes, defaulting to 12.5 is very odd. The model you referenced is a 12.0x model, so it's odd that your board is upping it a half step.

This is the one I have. It shows 2500mhz? which is 12.5 @ 200.

http://products.amd.com/en-us/Deskto...&f9=&f10=&f11=


Ah... just found this...

The Socket AM2 AMD Athlon64 X2 4800+ processor comes clocked at a cool 2.5 GHz, with a 12.5x CPU clock multiplier (12.5 x 200 MHz = 2500 MHz). Each core in this dual core Athlon64 X2 4800+ CPU has a 128KB L1 cache along with a 512KB L2 cache. This is a bit different from what AMD did with its Socket 939 series Athlon64 X2 4800+, it ran at 2.4 GHz and had 1MB L2 cache per core.

[Particle]

Hmm. When I looked it up a couple days ago I saw the 4800+ listed as a 2400MHz CPU.

http://www.xbitlabs.com/articles/cpu...2_4.html#sect0

To be fair, AMD did have a tendency to use the same number for multiple processors back in those days. I didn't look up your motherboard to know you had the AM2 version.

[ramman949]

Hmm. When I looked it up a couple days ago I saw the 4800+ listed as a 2400MHz CPU.

http://www.xbitlabs.com/articles/cpu...2_4.html#sect0

To be fair, AMD did have a tendency to use the same number for multiple processors back in those days. I didn't look up your motherboard to know you had the AM2 version.

NP! I appreciate all the help anyhow. Now Ive got to run some benchmarks and stability testing to see which one of those settings will work best.


Thanks again!!!

[cbjaust]

This is the one I have. It shows 2500mhz? which is 12.5 @ 200.

http://products.amd.com/en-us/Deskto...&f9=&f10=&f11=


Ah... just found this...

The Socket AM2 AMD Athlon64 X2 4800+ processor comes clocked at a cool 2.5 GHz, with a 12.5x CPU clock multiplier (12.5 x 200 MHz = 2500 MHz). Each core in this dual core Athlon64 X2 4800+ CPU has a 128KB L1 cache along with a 512KB L2 cache. This is a bit different from what AMD did with its Socket 939 series Athlon64 X2 4800+, it ran at 2.4 GHz and had 1MB L2 cache per core.

That is correct your CPU is a Brisbane (G1 or G2 revision 65nm chip with 512K L2 - most likely G2; ADO4800IAA5DO). there are two more "4800+" both 90nm and 2x1M L2, one S939 ADA4800DAA6CD "Toledo" E6 stepping core and one AM2 ADA4800IAA6CS "Windsor" F2 stepping. The Winsor one was also available as a 65W TDP version - ADO4800IAA6CS. All the 90nm ones have default multiplier of 12 for a 2.4GHz nominal clock speed.

So, so far there have been 5 different versions of 4800+ CPUs that AMD has made.

The Brisbane 4800+ I have here is not quite 100% stable at 11 x 271 = 2981MHz with the memory at 497MHz (994 DDR) CL5-5-5-15 2T. I think that the Brisbane IMC is not as good as the earlier Windsor and perhaps Toledo ones as I run into memory errors when I push the memory much more than 500MHz and the memory is PC8500 CL5 Team Xtreem Dark that I bought of someone who ran it in an intel system and they said it was good for 530MHz.

Oh well I will find out if the memory is any good when I do a domino upgrade with a PII 940 for my 6000+ which will replace the 4800+.

Cheers