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Intel Core i7 980X - guide to optimal cpu vtt & vdimm voltages Uncore to Memory frequency ratios - i4memory.com - different look at memory
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Old 20-04-2010, 08:41 PM   #1
eva2000
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Talking Intel Core i7 980X - guide to optimal cpu vtt & vdimm voltages Uncore to Memory frequency ratios

Thought I'd start a dedicated thread for this rather than get lost in Core i7 980X Club results thread.

Basically, Core i7 980X gulftown 32nm cpus changed some of the rules of the overclocking and voltages game a tad when it comes to absolute max safe for Vcore, VDIMM and CPU PLL voltages compared to Core i7 9xx series bloomfield 45nm cpus.
  1. Core i7 980X gulftown can utilise a lower uncore to memory ratio of 1.5x compared to Core i7 9xx series bloomfield's 2.0x ratio. Meaning you can theoretically use lower uncore multiplier and frequency and thus in theory push bclk a tad higher and/or use less cpu vtt.
  2. Core i7 980X absolute max voltages as per intel specs were lowered for 32nm cpus compared to bloomfield from 1.55v vcore to 1.40v, from 1.875v to 1.80v for vdimm
  3. Rumours going round though that >1.4v CPU VTT might be more dangerous to Core i7 980X, than Core i7 9xx bloomfield 45nm parts even though Intel spec sheet says Core i7 980X has a higher absolute max CPU VTT. So until Intel and other reviewers/experts come up with proof or otherwise, probably for 24/7 keep CPU VTT <1.4v for Core i7 980X. Personally, I'm comfortable with Core i7 980X and up to 1.4875v CPU VTT for benching only.

Absolute max voltage/current from intel datasheet pdfs, compare for Core i7 980X vs Core i7 900 series (i7 920 to i7 975)

Core i7 980X


vs

Core i7 900 series




Optimal CPU VTT voltages in relation to Uncore to Memory ratio

This theory is just from my limited experience with one sample of Core i7 980X B1 Step 2 engineering sample 3951A763 batch cpu and builds on my experience with Core i7 9xx bloomfield cpus I'd tested (8 cpus).
  • If you're pushing uncore frequency too high in relation to your mem frequency (uncore to mem ratio >2.0) - higher you push uncore frequency the higher the voltages needed for CPU VTT and VDIMM. That's just for 6GB configs, for 12GB the CPU VTT/VDIMM requirements would be potentially even higher - for more 12GB tips check this thread.
  • 980X only needs 3:2 ratio instead of 2:1 for 9xx series bloomfield cpus for uncore to mem frequency. From my testing so far on memory side on 980X while lower than 2:1 ratio for uncore:mem frequency allows less cpu vtt and vdimm to be used, on some X58 boards such as my Asus P6T6 WS Revolution, the uncore frequency is tied to RTL A/B/C channel values (round trip latency) so lowering uncore frequency will lower the RTL A/B/C values thus tighten latencies and performance but require more CPU VTT and VDIMM - this is especially the case with 3:2 uncore to mem ratio (where uncore frequency is 1.5x times that of mem frequency).
  • Of course, if you have a X58 motherboard with bios able to properly set RTL A/B/C channel values independent of uncore frequency, you can always lower uncore to mem ratio closer to 1.5x BUT then additionally manually loosen RTL A/B/C channel values (higher value = looser settings), i.e. delay of 4-8 so if set to RTL values in low 50s i.e. 51/52 might set to delay 4 or 6 to the RTL values in 57-60 range - you loose some performance though but if you want less CPU VTT and VDIMM used, it's one configuration to look at.
  • The same higher CPU VTT and VDIMM requirement occurs when you push uncore to mem frequency higher than 2:1 ratio (so when you set uncore frequency to >2x mem frequency). Examples for Xeon W3520 and i7 920 threads illustrate this. So basically for 980X setting uncore to mem frequency ratio at 1.5x and >2.0x will both require higher CPU VTT and VDIMM voltages, but setting to between 1.66x and 1.84x ratio MAY lower the CPU VTT and VDIMM memory requirements just depends on what your motherboard auto sets for RTL A/B/C values when you adjust the uncore multi and this uncore frequency in relation to mem frequency.
  • Using SYF_Karma's configuration as an example:



    In this case uncore = NB in cpuz mem tab of 3316 / 2x796 mem frequency = 2.08x uncore to mem ratio, so you'd probably need more CPU VTT and VDIMM than usually required. If you don't want to use too much CPU VTT and VDIMM, from my very limited testing so far, best to use a uncore frequency multiplier = ((2x memory multi) - 2) within -1 or + 2.

    So in SYF_Karma's case he's using 12x mem multi, so uncore set to ((2x12) -2) = 22x uncore multi or range between 19x to 22x uncore multiplier. Depending on cpu mem controller and memory, the required CPU VTT voltage difference from the usual 2x mem frequency uncore multi of 2x12 = 24x and that of 20-21x uncore multi is around ~0.06v volts. So you can probably use 0.06v less CPU VTT at 20-22x uncore multiplier compared to that at 24x uncore multiplier for 12x mem frequency.

Summary:

So for 12x mem multi on Core i7 980X safe uncore multipliers would be using formula

Safe uncore multiplier = ((2x memory multi) - 2) within -1 or + 2
  • 19x uncore multi = 19/12 = 1.58x ratio
  • 20x uncore multi = 20/12 = 1.66x ratio
  • 21x uncore multi = 21/12 = 1.75x ratio
  • 22x uncore multi = 22/12 = 1.83x ratio

For 14x mem multi on Core i7 980X safe uncore multipliers would be
  • 25x uncore multi = 25/14 = 1.79x ratio
  • 26x uncore multi = 26/14 = 1.86x ratio
  • 27x uncore multi = 27/14 = 1.93x ratio
* 28x uncore multi not included as it would be 2:1 ratio where less CPU VTT/VDIMM voltage isn't possible.

So for 12x mem multi might try between 22-23x uncore multi instead of 24x. For 14x mem multi might try 26-27x uncore multi instead of 28x uncore multi. For 8x mem multi might try 15x uncore multi instead of 16x uncore multi.

Of course, you have to take into account cpu bclk used, higher the bclk, the more CPU VTT needed as well. For example 200blck with 8x mem multi for DDR3-1600Mhz mem speed would probably require more CPU VTT than 133bclk with 12x mem multi for DDR3-1600Mhz speeds. Same can be said for 200bclk with 8x mem multi and 16x uncore multi requiring more CPU VTT/VDIMM than 200bclk with 8x mem multi and 14-15x uncore multi or 133bclk with 12x mem multi and 24x uncore multi requiring more CPU VTT/VDIMM than 133bclk with 12x mem multi and 22-23x uncore multi.

Just practical theory on my part for now from my experience. Would be nice if others can test and confirm

Last edited by eva2000; 28-05-2010 at 03:58 AM.
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Old 20-04-2010, 08:41 PM   #2
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Update: May 28th, 2010
This is an update to the above info as to further illustrate the new Uncore to Memory ratio requirements for Core i7 980X, and is apart of the i7 980X review I'm still writing (yeah taking ages to do )

As per the guide I wrote at above, Core i7 980X differentiates itself from it's Core i7 900 series Bloomfield siblings, in that the minimum required Uncore to DRAM memory frequency ratio was lowered from 2.0x to 1.5x. This means for Core i7 980X, you can potentially push base clock (bclk) and memory frequencies higher than that of Core i7 900 series Bloomfield cpus by using a Uncore to DRAM memory frequency ratio lower than 2.0x.

Let's first look at the basics for overclocking Core i7 cpus, then look at the specifics related to Core i7 980X Gulftown cpus.

Overclocking Intel Core i7 cpus:


When raising the base clock (bclk) to overclock the cpu, you're effectively raising cpu core mhz, qpi frequency, uncore frequency and memory frequency. As you raise those 4 components you need the right amount of
  1. vcore for cpu
  2. cpu vtt (uncore) for uncore frequency, qpi frequency and bclk
  3. vdimm for uncore frequency and memory frequency.

Most Core i7 cpus have upper ceiling limit for QPI and Uncore frequencies. Beyond this ceiling limit, you'll start requiring higher voltages or better cpu cooling (sub zero) to clock QPI and Uncore frequencies higher. The ceiling is ~4000mhz for QPI and Uncore frequencies. The ceiling limit can vary depending on how good the individual cpu is as well as the design of the motherboard used. The ceiling also seems to be effected by the type of memory ICs used as well, from experience you tend to be able to push higher with Elpida 50nm Hyper memory ICs than with say Micron, Samsung or Powerchip memory ICs. As with such factors the range of CPU VTT voltages required to hit 4000Mhz QPI and Uncore frequencies can vary from 1.21v to 1.65v - my personal experience has been between 1.35v and 1.5v CPU VTT voltages.

Why is it important to understand the above information ? It's important as understanding this allows you to overclock your Core i7 cpu more effectively. If you're not an extreme overclocker pushing insane voltages and using extreme sub zero cooling, and want the best 24/7 everyday settings, then you'd want to keep voltages as close to Intel specifications but still want better than default stock performance. If you're an extreme overclocker, you'll want to understand this to overclock your Core i7 cpu as efficiently as possible - so just the right amount of voltages needed for the task at hand.

Overclocking Intel Core i7 980X Gulftown cpus


The focus here is mainly of memory side as the Core i7 cpus have integrated memory controllers on the cpu itself, so to efficiently overclock the Core i7 980X Gulftown cpus, you need to understand the memory side. Otherwise, you could be overclocking and pushing bclk on the cpu and not realizing how raising bclk effects, QPI, Uncore and DDRAM memory frequencies.

It would be best to illustrate this with an example as to how the Core i7 980X Gulftown's lower Uncore to DDRAM memory frequency ratio effects overall system overclocking. I'm currently test how well 6GB Kingston 2000CAS8 KHX2000C8D3T1K3/6GX kit scales in terms of overclocked memory frequency for 8-8-8-24 1T timings at fixed 1.45v CPU VTT and 1.66v VDIMM voltages on Core i7 980X with 23x cpu multiplier and 12x memory multiplier.

If I was to observe the old Bloomfield Uncore to DDRAM memory frequency ratio requirements of 2.0x, I would need to set Uncore frequency multiplier to 24x (which is 2x times the 12x memory multiplier). At such settings, Kingston 2000CAS8 KHX2000C8D3T1K3/6GX kit managed to hit DDR3-2064Mhz 8-8-8-24 1T at 1.45v CPU VTT and 1.66v VDIMM with Uncore frequency at 4128Mhz. Pushing memory frequency any higher on the old Core i7 900 series Bloomfield cpus, you'd probably need to raise both CPU VTT and/or VDIMM memory voltages - remembering that VDIMM memory voltages need to be within 0.5v of CPU VTT voltage set to keep the cpu safe and working optimally.

But now Core i7 980X Gulftown allows for lower than 2.0x Uncore to DDRAM memory frequency ratios down to minimum 1.5x ratio. This means that you can lower Uncore frequency multiplier and either use less CPU VTT voltages for 24/7 or for extreme overclockers allowing you to potentially push memory overclocks much higher at the same CPU VTT and VDIMM memory voltages. Of course, the effect of lower Uncore frequency multiplier is reduced clock for clock performance.

Back to Kingston 2000CAS8 KHX2000C8D3T1K3/6GX scaling tests, when I reduced the Uncore frequency multiplier from 24x to 23x - I reduced the Uncore frequency from 4128Mhz to 4071Mhz. I knew I'd get a potentially higher max memory clock at 8-8-8-24 1T timings, but was surprised by how much extra. I managed to jump from DDR3-2064Mhz to DDR3-2124Mhz at the same voltages of 1.45v CPU VTT and 1.66v VDIMM.

6GB Kingston 2000CAS8 KHX2000C8D3T1K3/6GX
@DDR3-2124Mhz 8-8-8-24 1T at 1.66v
  • 23x 177bclk = 4071Mhz cpu frequency
  • 23x 177bclk = 4071Mhz Uncore frequency (cpuz reports it as NB frequency)
  • 18x 177bclk = 3186Mhz QPI frequency
  • 12x 177bclk = DDR3-2124Mhz memory frequency



6GB Kingston 2000CAS8 KHX2000C8D3T1K3/6GX
@DDR3-2230Mhz 8-8-8-24 1T at 1.66v


Managing to use TurboV to push bclk incrementally until I reached DDR3-2230Mhz 8-8-8-24 1T at 1.45v CPU VTT and 1.66v VDIMM !
  • 23x 186bclk = 4275Mhz cpu frequency
  • 23x 186bclk = 4275Mhz Uncore frequency (cpuz reports it as NB frequency)
  • 18x 186bclk = 3345Mhz QPI frequency
  • 12x 186bclk = DDR3-2230Mhz memory frequency



6GB Kingston 2000CAS8 KHX2000C8D3T1K3/6GX
@DDR3-2184Mhz 8-8-8-24 1T at 1.66v

Next step was to drop the Uncore multiplier one more step from 23x to 22x. You'd think this would by default allow higher memory clocks, but it didn't. The reason being on Asus P6T6 WS Revolution, Uncore frequency is tied to Round Trip Latency (RTL) A/B/C channels and auto adjusts to tighter RTL values as you lower the Uncore multiplier. For further reading on this check out the info about optimal Uncore to DRAM memory ratios for Core i7 980X. Dropping Uncore multiplier from 23x to 22x with 12x memory multiplier resulted in RTL values being too tight around 56 for the memory frequency involved and resulted in system not booting.

So next step is to manually loosen RTL A/B/C channel values with Uncore multiplier dropped from 23x to 22x. I used a RTL delay on channels A/B/C of 9, which resulted in RTL values around 65 and higher being set which allowed windows to boot in and pass single Super Pi 32M run @DDR3-2184Mhz 8-8-8-24 1T at same 1.45v CPU VTT and 1.66v VDIMM ! And ended up max screenshot captured clocks at DDR3-2305Mhz 8-8-8-24 1T at same voltages.
  • 23x 182bclk = 4186Mhz cpu frequency
  • 22x 182bclk = 4014Mhz Uncore frequency (cpuz reports it as NB frequency)
  • 18x 182bclk = 3276Mhz QPI frequency
  • 12x 182bclk = DDR3-2184Mhz memory frequency



6GB Kingston 2000CAS8 KHX2000C8D3T1K3/6GX
@DDR3-2305Mhz 8-8-8-24 1T at 1.66v

  • 23x 192bclk = 4418Mhz cpu frequency
  • 22x 192bclk = 4226Mhz Uncore frequency (cpuz reports it as NB frequency)
  • 18x 192bclk = 3457Mhz QPI frequency
  • 12x 192bclk = DDR3-2305Mhz memory frequency



So to keep voltages in check, you could lower your Uncore to DDRAM memory frequency ratio below 2.0x to reduce your CPU VTT voltage requirements below Core i7 980X's safe Intel spec max of 1.4v and still be able to potentially push your memory frequencies higher. Of course, there's other factors to consider such as Round Trip Latency (RTL) values which on some motherboards auto adjust based on Uncore frequency set - for more info on this read this thread.

System:
  • Intel Core i7 980X 3951A763 B1 Step 2 ES
  • EK Supreme LT H20 + TFC480 + MCP655
  • Asus P6T6 WS Revolution 0609 beta bios
  • Sapphire HD5970 OC Edition 10.4 Official Catalyst Drivers
  • 6GB Kingston 2000C8 (KHX2000C8D3T1K3/6GX)
  • 750GB Samsung SATAII OS
  • 120GB OCZ Vertex SSD (DATA)
  • Pioneer DVR216 Burner
  • Corsair HX1000
  • WinXP Pro SP3 nlite + Windows 7 Ultimate 64bit RTM (fully updated) dual boot OS

Last edited by eva2000; 29-05-2010 at 11:37 PM.
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Old 26-04-2010, 12:37 PM   #3
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"12x mem multi, so uncore set to ((2x12) -2) = 20x"

I think that should equal 22x
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Old 27-04-2010, 10:23 PM   #4
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Thanks Tim, hope it helps you out
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Old 09-05-2010, 11:50 PM   #5
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What can anyone suggest for pushing maximum uncore freq for super PI 32m

I cannot seem to push my uncore freq, pushing vvt hasn't helped.

Suggestions......
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Old 10-05-2010, 12:00 AM   #6
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Uncore frequency depends on
  1. CPU VTT volts (and to some extent the motherboard's CPU VTT power circuit design)
  2. VDIMM volts - you need memory that is able to scale as you push VDIMM volts up
  3. CPU memory controller quality
  4. Memory module's ICs used - Elpida Hyper ICs used in Dominator GT modules capable of 1600mhz 6-7-6-x and 2000+ 7-8-7-x tend to be able to push bclk, uncore and mem frequency higher.
  5. CPU and Memory cooling - colder the cpu = higher uncore frequency
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Old 10-05-2010, 12:24 AM   #7
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Thanks Eva, I am on the right track, I need to keep tweaking.

Classified, Kayl SS, Gt Dom 1866 , I have the right components, although I wish my 980x had a imc like my 3845B010
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Old 18-05-2010, 11:42 PM   #8
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hey

thanks for using mine as example of why not to get 12gb ram LOLOLOLOLOL
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