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Learng curve getting the better of me

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  • Curve
  • Overclocking
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March 10, 2010 10:50:27 AM

Hi,

I am trying to understand the following relationships (and looking for an overall idiots guide to help with the steep OC learning curve) (using Q6600 on Asus P5KC 35 board) :

CPU Processor FSB = 400Mhz
Number of cores = 4
Rated FSB = 1600Mhz

My motherboard only supports FSB of 1333Mhz so how can this work? So from my understanding I would be limited to 333 * 4 cores = 1333Mhz

333 x 9 mulitplier = 3Ghz

Is RATED FSB completely different to the FSB of the MOBO. i.e. is the MOBO FSB bus speed the allowable speed per stream?

So i am either trying to run 1600 through a 1333 channel...or I am completely not grasping this and the correct situation is in fact....

400 Mhz going up to the RAM, which can process 2 streams (800Mhz) so streaming back 2 streams at once 800Mhz

Meaning I am only using 800 of the allowable 1333Mhz



The RAM i am using is Corsair 6400C4 4-4-4-12

To run at a 1:1 ratio my FSB should be 400Mhz as the ram processes 2 streams at once...so we effectively get 400 x 2

So if I was to run at 333Mhz (rated FSB 1333Mhz) then the RAM ratio would be 5:6 ....or 333 : 400

And so i would understand this to mean there is excess bandwidth in the RAM, i.e. it could handle more than we are throwing at it


How would the ratios then work for DDR3 RAM

I have read article after article talking about the advantages of running 4-4-4-12 or 5-5-5-15 RAM etc...at lower and higher frequency. This does not mean a great deal to me as i do not understand the relationship between the timings and the Mhz of the RAM. Is there BASIC explanation anywhere. Explaning the theory behind it, and the relatinships between timings and RAM Mhz...and the realationship between RATED FSB of processor....the FSB of mobo...and how the two interact with RAM


Regards

Luke

More about : learng curve

a b K Overclocking
March 10, 2010 1:24:47 PM

lmartinefc said:
My motherboard only supports FSB of 1333Mhz so how can this work?

You don't have to worry about this at all, I had (until a few months ago)a P5KC MB and had the FSB up to 2100 so this won't limit your OC at all. You ram may, depending on how high you can OC it. When I build my computer I installed DDR2-800 memory in it and found the P5KC wasn't very OCable with the ram I had, so I then installed DDR2-1066 ram and that worked out much better. I never did try DDR3 memory in the board, but it would be the way to go as far as higher OC's are concerned so you wouldn't be ram limited.

Ton's of OCing guides on the net just google.

March 10, 2010 1:37:00 PM

This is where I am confused. The 'rated' FSB is reading 1600Mhz. How is this calculated?

I know that the FSB set in bios is 400Mhz...so this is being sent to the DDR RAM which is returning 800Mhz....

So I am within tolerance....i.e. its fine until the RAM reaches 1333Mhz (which is the motherboard limit)

So what is this 'rated' FSB

I am trying to educate myself as much as possible. Especially with regards to voltages.

Cpu V
NB V
SB V
VTT FSB

then in the power section of the BIOS there is a VCORE (is this the true voltage of the CPU?)

Overall looking to understand how the buses work.. and how the 4 different voltage element contribute to eachother.

Apologies if very noob. Sure a pic would paint a thousand words.
Related resources
a b K Overclocking
March 10, 2010 3:28:16 PM

Your FSB works like this you set it to 400 now to get your bus speed it quad pumps it 4x400=1600 The 400 is also multiplied by whatever the CPU multiplier is in your case its 9 so 9x400=3600 or 3.6ghz.

For your ram speed you are running at a 1:1 ratio so the base frequency for your ram is 400mhz now remember your ram is DDR (Double Data Rate) so 2x400=800. Now most ram will not go to far over its rated speed so if you have DDR2 800 ram you wont be able to overclock it much more then 100mhz.


Core clock 3600 mhz -- 9x400=3600
FSB 1600mhz -- 4x400=1600

Cpu V This is for your vcore of the CPU you will need to play with this if you have stability issues. Intel recommends not going over 1.5volts.

NB V Keep this one on auto for the most part. It controls the voltage for you memoery controller and the PCI-E also known as northbridge.

SB V Keep this one on auto also. This is for the South Bridge also known as the I/O Controller Hub. Controls the PCI slots, SATA and just about any I/O.

VTT FSB Keep this on auto too. System Bus Input Supply Voltage, often referenced as FSB termination voltage (VFSB) simply the voltage the fsb is running on. logic levels on the fsb are relative to this voltage. higher vtt results in higher logiclevels and thus in increased noise ratios. increasing vtt might help overclocking


In the Power section that shows what the Vcore is at that moment.
March 10, 2010 3:33:53 PM

Hi,

Thanks for this. Still confused

If im running 4 cores @ 400Mhz...this is a rated FSB of 1600Mhz...so how can a motherboard with a 1333Mhz FSB limit accomodate this. Or is this limit per channel? i.e. I can run RAM up to 1333Mhz (DDR3), or an individual core up to 666Mhz going out at 666Mhz, and receiving DDR back at 1333Mhz

I can run stable 3.2Ghz @ Cpu V 1.4V. This seems very high based on what I have seen other can acheive.

So thinking to change the RAM from tight tolerance of 4-4-4-12 to 5-5-5-12. Not sure exactly what this means though?

All this info is great so far guys

Regards

Luke
March 10, 2010 3:36:50 PM

Sorry, further form last. Temps are not an issue. Runs less than 50 even under Prime95 load. But unstable at less than 1.4V

Thinking RAM may be an issue. Seen other with VERY low Cpu Voltage, with relatively high NB and VTT?

How do these various voltage settings interact with eachother?
a b K Overclocking
March 10, 2010 3:41:28 PM

the lower the number the faster it is when it comes to the timings 4-4-4-15 is faster then 5-5-5-12.
March 10, 2010 3:43:51 PM

But i guess when overclocking 5-5-5-15 is more stable

(did you typo 5-5-5-12? Thought the last character had to be greater than the product of the previous 3?)
March 11, 2010 8:44:51 AM

hardwaresecrets! amazing!

answers all of my questions in detail. It's all well and good understanding how to run ratios etc...but this gives a great explanation as to the theory and how the system actually works....

Thanks

Luke
a b K Overclocking
March 11, 2010 9:53:43 AM

lmartinefc said:
Hi,

Thanks for this. Still confused

If im running 4 cores @ 400Mhz...this is a rated FSB of 1600Mhz...so how can a motherboard with a 1333Mhz FSB limit accomodate this. Or is this limit per channel? i.e. I can run RAM up to 1333Mhz (DDR3), or an individual core up to 666Mhz going out at 666Mhz, and receiving DDR back at 1333Mhz

I can run stable 3.2Ghz @ Cpu V 1.4V. This seems very high based on what I have seen other can acheive.

So thinking to change the RAM from tight tolerance of 4-4-4-12 to 5-5-5-12. Not sure exactly what this means though?

All this info is great so far guys

Regards

Luke



A little off base here, the number of cores the CPU has, has no bearing at all on bus speed. Did you get the answers you were looking for?
March 11, 2010 10:53:42 AM

Hmmm not really...

I thought the Bus speed was the speed between the CPU - NB - RAM...

So if my CPU is running at 400Mhz - NB - RAM processes at double rate and sends back 800Mhz

So the amount of bus being utilized is 800Mhz (well within the 1333Mhz limit)

So was wondering if this mobo limit is the limit per channel or the overall limit (i.e. 4 cores @ 400Mhz = RATED 1600Mhz)

I am confused as to the RATED FSB vs...MOBO limit

Just trying to clear up my understanding.
March 11, 2010 10:57:07 AM

And also... what is the real world (basic) explanation of how 4-4-4-12 or 5-5-5-15 or 5-5-5-18 would function. I can set it to this, but dont understand why I am setting it (or loosening it)... and i feel understanding is the key going forward.

5-5-5-15 = more cycles = more stable

lower ratio e.g. 333Fsb = 666Mhz RAM ... but RAM set to run at 800Mhz = 5:6 ratio so Mhz are being wasted...but system is more stable.

How could anyone run at a 4:3 ratio? Surely the CPU would then be limited by the RAM?
a b K Overclocking
March 11, 2010 2:27:16 PM

lmartinefc said:
And also... what is the real world (basic) explanation of how 4-4-4-12 or 5-5-5-15 or 5-5-5-18 would function. I can set it to this, but dont understand why I am setting it (or loosening it)... and i feel understanding is the key going forward.

5-5-5-15 = more cycles = more stable


Once again: http://www.hardwaresecrets.com/article/26/1

It explains what each of the numbers means and does and how it affects performance.

Once again if your P5KC had a FSB LIMIT of 1333 mhz how in the world did I push mine to 2100? Your ram will be the limiting factor not your FSB and yes I do understand you are trying to figure out the inner workings of your computer so you can intellectualize your actions, but finding someone to spend the massive amount of time to teach you this will be difficult at best. Google would be a valuable asset to you.

March 11, 2010 2:51:40 PM

Hi,

Read those articles...they are fantastic! Explain in all the detail I require

Found that the mobo FSB rating is normally the CPU limit i.e. the RATED FSB Limit. Alot of board specify 1333, 1600 etc...(like the P5 Deluxe goes up to 1600)

My P5KC takes 1600 ok (8x400Mhz) and runs stable with the following :

Vcc 1.4v
NB - auto
VTT FSB - auto

RAM 4-4-4-12 @ 2.1v (spec from manufacturer)

Can clock it to 3.6 but crashes under load.

Going to adjust the RAM to 5-5-5-15 and run memtest+ on it, see if I have a RAM issue

Or might remove 2 sticks - I am running 4 x 1Gb...not sure why number of sticks would have an effect (cant find any lit on this)
a c 197 K Overclocking
March 12, 2010 9:03:22 AM

Four sticks put more load on the memory controller than two sticks. This is pretty much a motherboard problem. Some boards are worse than others. This may effect system stability.

There are about three ways of solving this problem:
1. Use two sticks of RAM.
2. Increase the RAM voltage. If DDR2, do not go over 2.2 volts.
3. Relax the memory timing. Go from 4-4-4-12 to 5's-15 or from 5's-15 to 6's-18.
March 12, 2010 9:40:35 AM

Thanks guys

Think the issue im having is Vdroop

I set the BIOS to :

8x400 = 3.2Ghz

Vcc - 1.4V
NB - auto
VTT FSB - auto

RAM 2.1v 4-4-4-12

This runs smooth and stable and does not crash under Prime95.

But to get 3.405Ghz stable...i set FSB to 378 x 9

But to get this even half stable I have to set the Vcc to 1.485V. This is reported in CPUz as being 1.42v (idle) then under load it drops to 1.32v (and subsequently crashes after an hour or so)

I think this is Vdroop..? i.e. under load it tries to draw more power from the PSU...and i either have a rubbish PSU or MOBO that lets the voltage drop below the minimum and become unstable?

Using the antec 500 PSU that comes with the Antec Sonata III case, and using ASUS P5KC mobo ?

(also what is VID that Core Temp reports...it say 1.3125v ?)
March 12, 2010 5:26:15 PM

Thanks RJR

I just updated the BIOS so have several new options available to me. First of I enabled LLC.

What have you set your NB and VTT FSB to?

Many thanks

Luke
!