# Prime95: A Quick & Dirty Guide To The Custom Settings



## tmunn

Have you ever heard something like "The NB is stressed the most during 512K FFTs. This happens about 2-3 hours into Blend"? Or, have you ever had Prime95 consistently fail on the same FFT size? Well, that's when the custom test comes in handy.

*Pre-set Modes*
We all know about the three pre-set modes available for Prime95: Small FFTs, In-Place FFTs, and Blend. Small and In-Place modes test the FPU and caches. Blend mode tests everything, including RAM.

*Custom Mode*
By selecting Custom, you have total control over which FFT size/s are run. In general, the smaller FFTs stress the CPU, while the larger FFTs stress the memory and chipset - with one exception, the "in place" FFT.

*What is an "in-place" FFT?*
An "in place" FFT is simply an FFT that is calculated entirely inside its original sample memory. In other words, calculating an "in place" FFT does not require additional buffer memory. - Source(#2.3)

Ok, so between the definition above and the fact that Prime95 labels the "In-place large FFTs" test as max heat, power, and _some_ RAM tested. We know that when the FFTs are "in place", the RAM and chipset aren't being tested all that hard, regardless of the FFT size.

*Conclusion*
Below are a few screen shots of different custom tests.

CPU Test









RAM & Chipset Test








Note: when not using the "in place" option, be careful not to set the "memory to use" too high. If it's set too high, the system will start to use the paging file which will not stress the RAM.

Oh noes...it's always failing at 512 FFT size and I don't want to wait two hours for blend to reach that test









or you could do something like this









Maybe this is common knowledge to most here? If not, this should give you a general idea of what to do.


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## TwoCables

Whoa, very nice. I like it so much that I reported this thread saying, _"I feel that this needs to be stickied"_ in the report_._









In other words, I didn't know this stuff, and now I'm extremely glad I do.


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## ITaoI

Should 3gb be entered in amount of memory to use for 4gb system? Or should i just copy and paste linx amount memory use during all test







since it usually leaves like 400-500mb left and memory usage at like 90%.


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## TwoCables

Quote:


Originally Posted by *ITaoI* 
Should 3gb be entered in amount of memory to use for 4gb system? Or should i just copy and paste linx amount memory use during all test







since it usually leaves like 400-500mb left and memory usage at like 90%.

If you're careful enough, then you can probably get it to use 3300, or maybe even 3350. This would be roughly 95-96%.


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## radaja

*tmunn*,very nice thread


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## tmunn

Quote:


Originally Posted by *ITaoI* 
Should 3gb be entered in amount of memory to use for 4gb system? Or should i just copy and paste linx amount memory use during all test







since it usually leaves like 400-500mb left and memory usage at like 90%.

You could use linx or the performance tab in windows task manager to calculate how much memory to use. Whatever you do, be careful not to go over, or the test may be run in vain.

Quote:


Originally Posted by *radaja* 
*tmunn*,very nice thread









Thank you.


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## onnetz

Great info. I've always just used blend for chipset and memory and small ffts for cpu.
Going by what you've posted I was able to determine that my nb needed more voltage. In turn was able to lower vcore.
Forgot that I had started running my ddr2 800 at 1066.


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## Shrimpykins

I am totally messing around with my overclock when I get home!

Great post! +rep!


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## saiyanzzrage

wow, excellent, i always just hit blend and crossed my fingers..but now i can actually see what is not stable and single it out, like either ram/nb or cpu!

thanks so much!

4.1 - 4.2 here i come! (hopefully)


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## saiyanzzrage

wait im confused...if nb is stressed the most at 512k FFT then why did you specify 2048 - 4096k fft to test ram/chipset?

if i want to test my nb stability, should i put 512k fft or the 2048 - 4096k??


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## tmunn

Quote:


Originally Posted by *saiyanzzrage* 
wait im confused...if nb is stressed the most at 512k FFT then why did you specify 2048 - 4096k fft to test ram/chipset?

if i want to test my nb stability, should i put 512k fft or the 2048 - 4096k??

The 512K thing is just a quote from a Phenom II guide. That quote used to be slung around the AMD forums quite a bit. I included it only because I thought most AMD overclockers would have read that line once before.

2048 - 4096k(not "in-place") is indeed the ram/chipset test.

The 512K thing is, I'm guessing, something exclusive to the Phenom II IMC. It was in a lot of guides, but never fully explained.


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## saiyanzzrage

Quote:


Originally Posted by *tmunn* 
The 512K thing is just a quote from a Phenom II guide. That quote used to be slung around the AMD forums quite a bit. I included it only because I thought most AMD overclockers would have read that line once before.

2048 - 4096k(not "in-place") is indeed the ram/chipset test.

The 512K thing is, I'm guessing, something exclusive to the Phenom II IMC. It was in a lot of guides, but never fully explained.

any AMD oc'ers can answer/clarify this for us?

to stress cpu-nb freq stability only and not the cpu, what fft size should we use on a custom test?

tmunn, thanks for the guide!


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## tmunn

Personally, I'd run a round of 448 - 640k(not "in-place"), just to be in accordance with the Phenom II guides. Then do a 2048 - 4096k(not "in-place") run.

Further, any clarification from anybody on the 512K thing would be much appreciated.


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## saiyanzzrage

i would assume the 8k fft not in place would work for either amd or intel to test cpu stability, right?

Basically, what im trying to get out of this is to see what settings to run prime95 at so i can single out what is causing the instability in my oc, whether i need to add volts to the cpu, or play with my cpu-nb voltage and freq

so it can save me from running blend for hours and single it out that way


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## radaja

2hrs of 20k seems to be the best at checking cpu vcore according to leeghoofd at madshrimps


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## saiyanzzrage

Quote:


Originally Posted by *radaja* 
2hrs of 20k seems to be the best at checking cpu vcore according to leeghoofd at madshrimps

cool, thanks for the info..according to tmunn's guide, they should be run as in place right?


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## tmunn

With 20k FFT, I don't think it matters much. However, if you want to be doubly sure the test is CPU centric as possible, then run it in-place.


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## Nawamin

Wow, thank you very much for this. I have been pulling my hair out for days now why my computer rebooting after hours in to the test. But now I am armed with the info you posted I can now narrow down the problem quickly.

Turned out that my VCORE was low by a few hundredth of a volt


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## PyroTechNiK

Very useful guide.







+1.


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## reaper~

Yup, very nice. Thanks OP for posting.... now I can see some light show on my AFP. lol


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## blackbalt89

my stock heatsink hates any form of P95 lol


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## Erick

Very useful guide, thanks.

I've been having some problems running p95, started to dislike it, always BSOD, but i understand, what and when im testing thanks. Still a lil but confused about the 512k and 2048-4096k thing but ok. I'll do both.

Thanks


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## TwoCables

If you always end up with a BSOD, then that's gotta be a sign of instability.


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## MMJA

Quote:


> Originally Posted by *Erick;13669129*
> Very useful guide, thanks.
> 
> I've been having some problems running p95, started to dislike it, always BSOD, but i understand, what and when im testing thanks. Still a lil but confused about the 512k and 2048-4096k thing but ok. I'll do both.
> 
> Thanks


How long can you test for before a BSOD?


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## Gecko

Really helpful info!

I do have one question, though. How long do I have to run the 512k tests to consider my RAM or NB stable?


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## tmunn

For just the 512k alone, 20-30min should be good.

Don't forget that switching from small to large FFT sometimes may reveal instabilities, that's where Blend mode comes in.


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## jgmaverick8

Alright so I am pretty much confused.. How am I to tell if a certain component needs more voltage or what not? Is there a clear indication during the test that my settings suck? Or do I just have to wait for it to crash...

nvm... im pretty sure just wait till it crashes


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## TwoCables

Quote:


> Originally Posted by *jgmaverick8*
> 
> Alright so I am pretty much confused.. How am I to tell if a certain component needs more voltage or what not? Is there a clear indication during the test that my settings suck? Or do I just have to wait for it to crash...
> nvm... im pretty sure just wait till it crashes


Usually, a failed stability test means the CPU's core voltage needs to be increased. However, if you are adjusting more than just the CPU's clock frequency, such as the memory frequency and memory voltage, then those variables must be looked at too. So generally, when you're just focusing on your CPU overclock, the first thing to do is increase its core voltage.

Although, it can depend on the system too. You may also need to adjust other voltages such as the FSB and/or northbridge voltages, but it's really a matter of experimentation.

You'll know your system isn't stable from a stability test in one of 3 ways:


You get a BSOD
Your system locks up
The stability testing program fails. In Prime95, one of the "workers" will stop with an error.

When any of these 3 happens, the first thing to do is try increasing the core voltage a little. It doesn't matter what kind of error your get in Prime95.

However, my best advice is to always seek assistance from Overclock.net by making a thread in one of the AMD forums on here (I noticed that you have an AMD system). Usually for general overclocking assistance, "AMD - General" is the best forum to use because it can pertain to either your CPU, motherboard, memory, or any combination thereof (or even all 3). However, if you are absolutely certain that it is your CPU, or your motherboard, or even your memory, then choose one of those AMD forums (for example, "AMD CPUs", "AMD Motherboards", or "AMD Memory").

I think I'm making this all seem more difficult than it really is, so my final advice is to relax and have fun.


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## jgmaverick8

Haha yeah it's kind of addicting so it is indeed fun. But I'm really glad I stumbled across this thread. Gonna run prime95 as soon as I get home. Thanks!


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## TwoCables

Quote:


> Originally Posted by *jgmaverick8*
> 
> Haha yeah it's kind of addicting so it is indeed fun. But I'm really glad I stumbled across this thread. Gonna run prime95 as soon as I get home. Thanks!


You're welcome!


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## JohnManko

Nice work dude! Please re-upload RAM & Chipset settings image, is missing.


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## tmunn

Done, and hosted them here this time so that it shouldn't happen again. Thanks for bringing it to my attention.


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## zluo4377

Hmm, can you please help me with the actual settings that I should go with?
I'm running a 3770k at 4.5 Mhz with 1.21v, and my ram is 2 x 8GB with stock mhz & speed.


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## nado4ilhas

When testing 16gb of RAM I need to select how many (memory to use)?


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## TwoCables

Quote:


> Originally Posted by *nado4ilhas*
> 
> When testing 16gb of RAM I need to select how many (memory to use)?


Multiply the amount of memory you have in Gigabytes by 1024. Then, multiply that number by .80 to .85 to get about 80 to 85% of your memory.

I apologize for not simply giving you the answer you wanted, but if you give a man a fish, then you feed him for a day. However, if you teach a man *how* to fish, then you feed him for the rest of his life.


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## blaze2210

Quote:


> Originally Posted by *TwoCables*
> 
> Multiply the amount of memory you have in Gigabytes by 1024. Then, multiply that number by .80 to .85 to get about 80 to 85% of your memory.
> 
> *I apologize for not simply giving you the answer you wanted, but if you give a man a fish, then you feed him for a day. However, if you teach a man how to fish, then you feed him for the rest of his life.*


Well said! This is getting added to my sig (after I clean up the mess that is my sig)....


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## TwoCables

Quote:


> Originally Posted by *blaze2210*
> 
> Well said! This is getting added to my sig (after I clean up the mess that is my sig)....


Nice.


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## blaze2210

Quote:


> Originally Posted by *TwoCables*
> 
> Nice.


Showing someone how to find the answer is definitely better than just giving the answer over. It's also more helpful for anyone who needs settings for their own system and has a different amount of memory.


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## TwoCables

Quote:


> Originally Posted by *blaze2210*
> 
> Showing someone how to find the answer is definitely better than just giving the answer over. It's also more helpful for anyone who needs settings for their own system and has a different amount of memory.


Indeed!


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## nado4ilhas

Quote:


> Originally Posted by *TwoCables*
> 
> Multiply the amount of memory you have in Gigabytes by 1024. Then, multiply that number by .80 to .85 to get about 80 to 85% of your memory.
> 
> I apologize for not simply giving you the answer you wanted, but if you give a man a fish, then you feed him for a day. However, if you teach a man *how* to fish, then you feed him for the rest of his life.


Hi,

16gb 4x4gb
my amount of memory *16.330mb*

I need to put that amount in prime95 custom

FFT size min (in k) 800k max FFT size (in k) 800k

memory to use (in MB) 16.330

16x1024= 16.384
16.384x 0.85=13.926

that's right?

thanks for the reply


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## TwoCables

Yep, you are using the correct mathematical equations (multiply by 1024 then divide that number by whatever percentage you want, like .80 or .85 or whatever, but I recommend staying at 85% or below).


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## Yomny

Super old thread to revive but was just thinking of creating something similar and found this.

I'm adding these links here but will probably copy and paste for easier viewing.

FFTs for specific testing

I'm getting some random shutdowns and it seems to be due to uncore instability. I've testing the CPU over clock and have past all tests thrown at it but when I start overclocking the cache, do some testing and passes but random shutdowns soon there after.

Trying to see what prime setting could help me test the cache portion. Thanks.


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