Calculate your A64 overclocking potential

[vanrossum]

You wonder what frequency your A64 can reach at a certain Vcore?

Well, I did, and tried to find a way to calculate it instead of doing the time consuming cycle of SuperPi/Prime95 after every voltage change over again. I will show you how to calculate and then afterwards why this calculation holds (roughly). edit-> PLEASE READ THOROUGHLY, it is not trivial! <-edit

1. Find the highest stable frequency "y" in Mhz, at a certain Vcore "x"
2. At some other "Vcore" the max. stable "Freq" is

Freq = y + (Vcore - x) * z (*)

z = 870 for Toledo (also dc-Opteron)
z = 860 for Manchester
z = 620(?) for SanDiego (also sc-Opteron)
z = 310(?) for Venice
z = 860 for Winchester

Notes:
a. Take the initial Vcore/Freq (x,y) point not too far from the point you aim for.
b. I only listed z values for 90mm A64 cores, as I did not include data from older cores like Clawhammer and NewCastle
c. The Venice and SD values for z seem too low to me. It was the most precise value I could obtain, but you might need a HIGHER value of about 800 (never tried it though). I expected all 90mm single-cores to behave about the same. A possible reason for Venice to be that low? (see below)
d. This relation should roughly hold if you manage to keep your CPU and MB cool and your PSU rails clean. Since the heat generated by the CPU grows linearly with the frequency and Vcore^2 and (*) is linear, it follows for the power of your PSU and the heat your CPU Cooler has to be able to carry away is:

Q ~ Freq^3 (**)

Here is a table for an imaginary setup with a Toledo. The first column contains the Vcore, the second the heat output relative to that at 1.4V, the third one contains the frequency that should be able to be reached about.

Vcore Heat freq_tol
[V] [%] [MHz]
---------------------------------
1.250 -28.8 2470.8
1.275 -24.5 2492.6
1.300 -19.9 2514.3
1.325 -15.2 2536.1
1.350 -10.3 2557.8
1.375 -5.3 2579.6
1.400 0.0 2601.3
1.425 5.5 2623.1
1.450 11.1 2644.8
1.475 16.9 2666.6
1.500 23.0 2688.3
1.525 29.2 2710.1
1.550 35.7 2731.8
1.575 42.4 2753.6
1.600 49.3 2775.3
1.625 56.4 2797.1
1.650 63.7 2818.8

--------------------------------------------------------------------------------------------------------------------------------
Why (*) should work for you?

All overclocking results in the databases on the internet give a nice sample that can be treated statistically.
I gathered the o/c results from these pages:

http://www.forumdeluxx.de/forum/showthread.php?t=204404
http://www.forumdeluxx.de/forum/show...teron+stepping
http://www.ocforums.com/showthread.p...08#post2987108
http://www.hwupgrade.it/forum/showthread.php?t=935362
http://www.xtremesystems.org/forums/...3&page=1&pp=25

, 591 in total. I categorized them as in (**), so I made no difference between opteron 165 or FX-60 for example, as both of them have Toledo cores.
Now if you assume that the extreme results roughly weigh out the too loose results, all elements of the compiled lists make up an average processor. As statistical treatment requires, I included all entries in the databases and didn't filter out dubious cases.

Here are some plots of the samples for the different cores, with linear-chi^2-fits. I chose a linear fit for simplicity.

1. Single-Cores


2. Dual-Cores


3. All fit-curves with four points measured at my own Opteron 165.


This picture shows, that the curves are nearly parallel. This actually is the most convincing argument that any processor overclocking potential can be calculated with these curves. Depending on the quality of your
1. die
2. cooling
3. mainboard
4. PSU
, your curve (the one that matches your processor) is like one of these, just shifted up or down. edit-> There apparently is more evidence for the linear relation to hold, as hitechbj1 pointed out (http://www.ocforums.com/showthread.p...06#post2588006):

How does Vcore improve CPU frequency?
When certain higher Vcore is applied to a CPU or any logic chip, the current, called Idsat, in transistors would increase, hence the transistors can operate the logic gates faster. The delay of a logic gate, transistor current (Idsat), voltage (Vcore), loading (Cload) are related by

delay = Vcore Cload / Idsat
Idsat = k (Vcore - Vt)^n

where Vt is transistor threshold voltage and k is some constant, n is between 1 and 2.
Simply speaking, the higher the Vcore, the higher the current Idsat, the smaller the delay (hence chips run faster).
It can be shown that for a given temperature and without temperature constraint, increase Vcore can speed up frequency about linearly, that is the higher the Vcore, the higher the max frequency.

frequency / Vcore ~ constant

<-edit

My Opteron 165 performs on air worse than the average Toledo core (see lowest picutre). However, that average is based on results from overclocking-freaks, that proudly present the returns of good hard labour. So don't be disappointed if your curve is below average.

[macg]

Useful stuff, did some computations and values are the same as in actual testing..

[nguyenquochuy]

hmm ! it's not exactly with my Venice 3000+ !

[vanrossum]

hmm ! it's not exactly with my Venice 3000+ !

Try z=310 first, if it does't work out try z=620 (as for sd), if that's still to low...

I expected z_venice = z_sd, but since the check is missing here, z_sd may be a bit different either.

Can you guys give the z-value you need for your Venice/SD, then I can refine the values in the 1st post.

[e-jump]

wow, statistics meets overclocking

good job...
sure a tough data gathering session, and to group few hundred samples..

well, some may say its not effectively true, but since its gathered from few hundred samples, its worth to be a guide

good job indeed

[nguyenquochuy]

my rig :
DFI LP UT NF4 SLI-DR Expert
AMD Athlon 64 3000+ (Venice Rev E6)
Corsair XMS TwinX1024-3200XL Rev 1.2
AcBel Intelligent Power 500W Gold
Cooling : Cooler Master Hyper 6+
here my oc result (all with 9x multiplier & 100% stable with SP2004) :
vcore in CPU-Z__________vcore set in BIOS__________HTT Bus (MHz)
1.36___________________1.375____________________25 7
1.376___________________1.4_____________________26 2
1.408___________________1.4*102.4%______________26 7
1.456__________________ 1.475____________________274
1.488___________________1.5______________________2 79
1.568___________________1.55*102.4%______________2 84
1.6_____________________1.55*104.8%______________2 89

i can reach 300 HTT with 1.65V in CPU-Z but it's not stable !
most of Venice 3000+ rev E6 cpus not good for oc ! from what i hear it's only stable at 2600 MHz !

sorry for my English !!!

[RTB]

Good stuff, the Venice is certainly an oddball. It may be the difference between E4 and E6 revisions that's causing it.

[Fr3ak]

Welcome to the forums vanrossum !
Nice statistics. Surely that took a while to figure it out.
Thats the best 1st post I have seen so far

[vanrossum]

Tnguyenquochuy:
hat yields z_ven=1120 for your case. We need more ones to make up for a mean z_ven.

But it does make it more likely, that we need z_ven =~ z_tol = z_man =~ z_sd

[nguyenquochuy]

to vanrossum : currently i've got an opty 146 CAB2E 0548 running at stock speed, i'll try it with your formula ! thanks guy !!!!

[v0dka]

I'm not a matematical wonder, but if I understand correctly there is a linear connection between raising Vcore and overclock frequency?

That's simply not true I think. Many preocessors (including mine) gain more relatively in the low Vcore segments. For example: from 1.4v to 1.5v you get 600Mhz more and from 1.5 to 1.6 yon get only 300 more. That's only half.

Correct me if I'm wrong please.

[Dragoran]

on my opteron 170 I did this:
it runs at 2700 / vcore 1.45(in sensors/ite sm etc.) and (1.45*1.048 in bios)
should I use 1.51 or 1.45 ?
using 1.51 it is like this:
2700+(1.60-1.51)*870=2778.3000000000002
using 1.45 it this:
2830.5
did I do anything wrong? I doubt that it will run @ 2830.5 because it was impossible to get it running at 2.8GHz
Cooler is Thermaltake Sonic Tower + 2x120mm fans (one in sandwich mode)
mobo: dfi nf4 lp dr-expert
psu: tagan 480W

[e-jump]

well, statistics isnt always accurate.
depends on how many samples taken into account..
but as we know, theres alot of factors that affects overclockability, esp motherboard used, psu, etc..

well, at least vanrossum put lotsa effort into gathering 500+ samples result O__o
we can see some pattern, and see our own result goes where

[Dragoran]

can't get it stable @2790Mhz
so either I did something wrong or this calculation isn't accurate...

[s7e9h3n]

lol...I decided to try something a little different...use this formula and figure out what's the max speed I'm able to be stable at using DEFAULT voltage on my opty....soooo - let's say I'm 32m stable @ 3753, 1.648Vcore and I'm trying to find out what speed I'm stable @ using 1.35Vcore -

Freq = 3753 + (1.35 - 1.648)*620.......

This gives me 3568.24Mhz stable @ default (1.35) voltage....hmmmmm....I don't think so (although there is a SLIGHT chance it may be close since I can run a 1m @ 3600, 1.48V)

[stone_cold_Jimi]

It's an interesting idea and thanks for the work that's gone into it. It probably needs fine tuning (more data) and I think phase-change might throw it a loop, but in principle it's the right way to go about being predictive.

[pcdoc1]

I see alot of new post just around the corner....

I bought my parts, built the box, ran the formula and entered the settings into the bios on the first boot. I heard 3 beeps and saw smoke coming from cpu area of the board. The machine never booted again. Could it be a problem with my ram, power supply? Is there anyone else having a problem running a 3000+ at 4250? What could be wrong?

Nice work though....

[PoL]

NICE!!
Worked with my X2 3800+.

[lawrywild]

I see alot of new post just around the corner....

I bought my parts, built the box, ran the formula and entered the settings into the bios on the first boot. I heard 3 beeps and saw smoke coming from cpu area of the board. The machine never booted again. Could it be a problem with my ram, power supply? Is there anyone else having a problem running a 3000+ at 4250? What could be wrong?

Nice work though....

trying to run a cpu higher than it can go doesn't blow it up

[pcdoc1]

trying to run a cpu higher than it can go doesn't blow it up

And no one said it did....

[vanrossum]

on my opteron 170 I did this:
it runs at 2700 / vcore 1.45(in sensors/ite sm etc.) and (1.45*1.048 in bios)
should I use 1.51 or 1.45 ?
using 1.51 it is like this: 2700+(1.60-1.51)*870=2778
using 1.45 it this: 2830

If you insert the x=1.51 bios, then take the 1.6V bios. You should be able to get 2778MHz with that. But remeber that you get 34% more heat output. Your cooler should be able to hadle that, otherwise you won't make it to 2778.

[tzitzos]

nice work man!!

works for me at +-10% speeds

try more than 3 cpu

[vanrossum]

To nguyenquochuy:
Here's a pic with your curve plotted in. It looks like your oc at low voltages is a bit loose. Did you try to get out the most at low voltages? Are you sure your Ram is not limiting you there (other devider maybe)?

Maybe your z_ven get's lower then, maybe your z_ven->870....

[vanrossum]

nice work man!! works for me at +-10% speeds. try more than 3 cpu

Make sure you can ignore your ram when maxing your FSB. Just choose a safe setting

[nguyenquochuy]

to vanrossum : RAM isn't the factor limiting me cos i adjust the divider at which RAM running at df speed (only oc cpu) !

It looks like your oc at low voltages is a bit loose.

maybe !......

thank guy !

sorry for my English !!!!