Swiftech
Page 36 of 138 FirstFirst ... 26333435363738394686136 ... LastLast
Results 876 to 900 of 3432

Thread: Core i7/X58 Overclocking Thread

  1. #876
    Xtreme Addict dejanh's Avatar
    Join Date
    May 2008
    Location
    Vancouver, BC, Canada
    Posts
    1,418
    Ok, I think I finally have some answers to the 20x multiplier instability and a number of other issues many users are complaining about. You will have to follow me here as this is not that simple, but it makes a lot of sense and all of my testing to date has actually confirmed it. I have spent a lot of time figuring this out and I really hope that this will help people. Indeed, I am now able to predict ahead of time what settings will POST, what settings will not, and approximately which component will need to be juiced up higher to result in a more stable system. Furthermore, this will be a very thorough overview of Core i7 overclocking that will expose some serious limitations, particularly on the i7 920 and i7 940 parts. It is all primarily linked to the Uncore and QPI speeds.
    First off, I will use the Core i7 940 for all of my examples. Core i7 920 and i7 940 are for all intents and purposes the exact same chip, but the i7 940 is just factory clocked higher. These are most likely not higher binned chips, and even if they are by some chance it really does not matter. You will soon see why. In essence, same holds true for the i7 965 EE though they are certainly higher binned and quite likely somewhat more forgiving when overclocking. The fact that they can overclock using an unlocked multiplier is a huge bonus for this chip.
    For details on each of the CPU specifications see Intel's website and tech specs/data sheets. I'll just briefly mention the specs here, for reference.

    Core i7 920 - 2.66GHz, 20x133MHz, 4.8GT/s QPI (2.4GHz), QPI multiplier 18x (18x133MHz)
    Core i7 940 - 2.93GHz, 22x133MHz, 4.8GT/s QPI (2.4GHz), QPI multiplier 18x (18x133MHz)
    Core i7 965 EE - 3.2GHz, 24x133MHz, 6.4GT/s QPI (3.2GHz), QPI multiplier 24x (24x133MHz)

    The key thing to remember here is that for Core i7 processors everything is interconnected, much like in case of AMD processors. Therefore, changing the BCLK speed affects everything from core speed, to QPI link speed, to Uncore speed, to memory speed. The key elements and the limiting ones here are the last three, the QPI link speed, Uncore speed, and memory speed. Particularly, the QPI is the limiting factor for the other elements as the highest stable QPI link speed for the current Core i7 processors is 8.0GT/s or 4.0GHz for 99% of systems out there. Some exceptions have been observed, but these are extremely rare. This may also be chipset dependent limitation and it is possible that newer chipsets supporting Core i7 will not have this limitation. Anyway, enough introduction. Let's get to the details.

    First let's look at the relationships between QPI, Uncore, and DRAM speeds.

    DRAM speed must be in a 1:2 ratio or less to Uncore speed which in turn must be in 1:1 or less ratio to QPI link speed (8:9 Uncore to QPI or lower is preferred as the more you approach 1:1 the more unstable the system becomes).

    So why Uncore to QPI ratio of 8:9?

    I derived this ratio from Intel's specifications on Core i7 processors. Highest supported memory for Core i7 is 1066MHz with a QPI of 4.8GT/s or 2.4GHz. According to processor specifications then, Uncore would be running at 2xDRAM (or 2x DRAM multiplier, in this case 16x) which results in an Uncore speed of 2132MHz. When you take the ratio of Uncore to QPI you will get 2132:2400 or approximately 8:9.

    I can run my Uncore higher than QPI and I am not seeing any problems. How come?

    This is possible. In my testing this proved to be less stable than keeping Uncore speed below that of QPI. However, more importantly I found that running Uncore and QPI in a ratio more than 8:9 and approaching 1:1 made the system quite unstable, especially with added stress when overclocking. Furthermore, it is quite likely that running QPI lower than Uncore results in some performance degradation (I did not test this however). Finally, it is important to note that this flexibility is in a large part not there on the non EE parts as you do not have control over core multipliers to the extent where you could be running Uncore very high and QPI link very low as was shown in this example:

    http://www.xtremesystems.org/forums/...79#post3491979

    As a general rule of thumb I did not want to test combinations that fall way outside Intel's specifications, that require voltages approaching critical values according to Intel datasheets, etc. Most users are looking to overclock but still run a long term stable system and not just get the highest benchmark score. Naturally, a lot of instability issues can be resolved by sufficiently increasing voltages to the components experiencing problems but this is very risky and not sustainable for long term use. To be safe I would strongly advise staying within the limits specified by Intel (can be seen here http:// www.xtremesystems.org /forums/showpost.php?p=3435336&postcount=13) and recommend staying at least a good percentage below the absolute maximums.

    Now that we know this relationship, let's dive right into some of the most common issues with Core i7 processors.

    1. Why is it that I cannot run my 2000MHz memory in my new Core i7 system?

    To understand this note the maximum QPI link speed we mentioned earlier. Using the simple ratio we defined, we can see that with the maximum QPI link speed of 4.0GHz we can have a theoretical maximum Uncore of 4.0GHz and a maximum memory speed of 2.0GHz. These however are only theoretical maximums and are by no means guaranteed. For starters, QPI and Uncore cannot be run at the same speed as any clock oscillations can result in a crash if the ratio of QPI to Uncore ever falls below 1:1. Therefore, Uncore must always be below QPI to avoid this, and preferably below the 8:9 Uncore to QPI ratio to guarantee stability. Consequently, if we cannot achieve 4.0GHz Uncore, this means that we absolutely cannot achieve 2.0GHz memory and we can therefore not guarantee any stability for 2.0GHz memory. Technically, the maximum DRAM speed for a stable system is equal to ((Max. Uncore) / (Safe QPI:Uncore Ratio)) / 2 or (4.0GHz / 9:8) / 2 = 1.777GHz. In between 1.777GHz DRAM and 2.0GHz DRAM you are likely to experience some level of instability over the long term. Past 2.0GHz you are just plain lucky.

    2. Why is it that almost none of the X58 boards can reliably clock the BCLK over 222MHz?

    The answer to this again lies in the QPI link speed. At default (and lowest possible multiplier) for QPI of 18x the QPI link speed becomes 18x222MHz or 3.996GHz (4.0GHz). As we have already stated earlier this is dangerously close to the maximum QPI link speed and is therefore very unreliable. Anything higher than 222MHz and you have exceeded the current QPI maximum so in 99% of cases you will experience no POST. For this matter, a simple guideline is that any BCLK combined with a QPI multiplier that is at or very near maximum 4.0GHz QPI link speed is a candidate for no POST or instability.

    3. What the heck is the deal with the 20x multiplier then?

    This one is a real kicker (in a funny way). Yes, 20x multiplier is special, in more than one way, but mostly in the way people are trying to use it. You see, there is nothing wrong with the 20x multiplier. Indeed, it works, just like all other multipliers, perfectly fine. It is the DRAM multiplier and BCLK that people are combining with it that causes problems when combined with the QPI multiplier and the Uncore speed. At 20x200MHz, our default memory multiplier is 8 and our memory is at 1600MHz. The Uncore speed becomes 16x200MHz or 3.2GHz (or 2xDRAM at minimum). Therefore, remembering our (safe) ratios of 8:9 Uncore to QPI we see that the QPI link speed must be a minimum of 3.6GHz or higher. In case of 20x200MHz the Uncore and QPI are exactly in this ratio and with the added stress on the core, cache, IMC, DRAM, etc. this becomes a problem. At this point clock oscillations become much more prominent and if the QPI link speed falls below the 9:8 ratio to Uncore at any point in time combined with the added stress on the components the system can and likely will become unstable. Hence, at 20x200MHz with a default memory, Uncore and QPI multipliers we cannot really have a 100% stable system. So you say "just up the QPI link speed then". Not so fast. Remember our multipliers for QPI? They start at 18x, and the next is 22x, and so on. Unfortunately, 22x200MHz results in QPI link speed of 4.4GHz which results in no POST. Therefore, this cannot be done. Indeed, the highest reliable BCLK for default multipliers when using 20x core multiplier is 181MHz which with a 22x QPI multiplier would result in 3.982GHz QPI link. Even if you could set QPI multiplier to 20x, this would still not work for 99% of the boards out there as your QPI link would still be 4.0GHz. So what is the solution you ask? Memory multiplier. It needs to be lower. 1600MHz DRAM is approaching the maximum stress point for 20x200MHz core settings as it pushes on the limits of Uncore and QPI too much. By using a lower memory multiplier (say 6x if possible) the DRAM speed would become 6x200MHz or 1200MHz, Uncore could then be set at 2.4GHz with a lower multiplier which would then allow the QPI link to stay at 18x and well below the QPI link limits but still in a stable ratio to the Uncore.

    So there you go. A couple of answers to some of the most painful Core i7 questions. Unfortunately, if you can read between the lines, this does not bode well for anyone owning a Core i7 940 or a 965 EE. For all intents and purposes Core i7 920 performance and Core i7 940 performance are identical. Core i7 965 EE has more flexibility but only because of its unlocked multiplier which allows it to use lower BCLK speeds and DRAM multipliers to achieve higher clocks. Otherwise, it is no different than a Core i7 920 or a Core i7 940. Like I said before, this may also be a chipset imposed limitation, and the processors themselves may be a lot better but at the moment, the state of the affairs is like this.

    I have put a lot of thought and work into this so please if you want to comment do it constructively. I welcome any feedback and I hope that this will help a lot of people. It has helped me now to have a rock solid 4-core/8-thread, full 64-bit instruction set 4GHz air-only overclock on the Core i7 940 combined with a nice 1800MHz on my Corsair Dominator triple-channel sticks while keeping all of the voltages within Intel's recommended settings (i.e., DRAM is below 1.65V, QPI/DRAM is below 1.4V, and Vcore is below 1.39V under 100% load).
    Last edited by dejanh; 12-17-2008 at 07:27 AM.

  2. #877
    Xtreme Mentor 003's Avatar
    Join Date
    Oct 2005
    Posts
    2,790
    Quote Originally Posted by dejanh View Post
    Ok, I think I finally have some answers to the 20x multiplier instability and a number of other issues many users are complaining about. You will have to follow me here as this is not that simple, but it makes a lot of sense and all of my testing to date has actually confirmed it. I have spent a lot of time figuring this out and I really hope that this will help people. Indeed, I am now able to predict ahead of time what settings will POST, what settings will not, and approximately which component will need to be juiced up higher to result in a more stable system. Furthermore, this will be a very thorough overview of Core i7 overclocking that will expose some serious limitations, particularly on the i7 920 and i7 940 parts. It is all primarily linked to the Uncore and QPI speeds.
    First off, I will use the Core i7 940 for all of my examples. Core i7 920 and i7 940 are for all intents and purposes the exact same chip, but the i7 940 is just factory clocked higher. These are most likely not higher binned chips, and even if they are by some chance it really does not matter. You will soon see why. In essence, same holds true for the i7 965 EE though they are certainly higher binned and quite likely somewhat more forgiving when overclocking. The fact that they can overclock using an unlocked multiplier is a huge bonus for this chip.
    For details on each of the CPU specifications see Intel's website and tech specs/data sheets. I'll just briefly mention the specs here, for reference.

    Core i7 920 - 2.66GHz, 20x133MHz, 4.8GT/s QPI (2.4GHz), QPI multiplier 18x (18x133MHz)
    Core i7 940 - 2.93GHz, 22x133MHz, 4.8GT/s QPI (2.4GHz), QPI multiplier 18x (18x133MHz)
    Core i7 965 EE - 3.2GHz, 24x133MHz, 6.4GT/s QPI (3.2GHz), QPI multiplier 24x (24x133MHz)

    The key thing to remember here is that for Core i7 processors everything is interconnected, much like in case of AMD processors. Therefore, changing the BCLK speed affects everything from core speed, to QPI link speed, to Uncore speed, to memory speed. The key elements and the limiting ones here are the last three, the QPI link speed, Uncore speed, and memory speed. Particularly, the QPI is the limiting factor for the other elements as the highest stable QPI link speed for the current Core i7 processors is 8.0GT/s or 4.0GHz for 99% of systems out there. Some exceptions have been observed, but these are extremely rare. This may also be chipset dependent limitation and it is possible that newer chipsets supporting Core i7 will not have this limitation. Anyway, enough introduction. Let's get to the details.

    First let's look at the relationships between QPI, Uncore, and DRAM speeds.

    DRAM speed must be in a 1:2 ratio or less to Uncore speed which in turn must be in 1:1 or less ratio to QPI link speed (8:9 Uncore to QPI or lower is preferred as the more you approach 1:1 the more unstable the system becomes).

    Now that we know this relationship, let's dive right into some of the most common issues with Core i7 processors.

    1. Why is it that I cannot run my 2000MHz memory in my new Core i7 system?

    To understand this note the maximum QPI link speed we mentioned earlier. Using the simple ratio we defined, we can see that with the maximum QPI link speed of 4.0GHz we can have a theoretical maximum Uncore of 4.0GHz and a maximum memory speed of 2.0GHz. These however are only theoretical maximums and are by no means guaranteed. For starters, QPI and Uncore cannot be run at the same speed as any clock oscillations can result in a crash if the ratio of QPI to Uncore ever falls below 1:1. Therefore, Uncore must always be below QPI to avoid this, and preferably below the 8:9 Uncore to QPI ratio to guarantee stability. Consequently, if we cannot achieve 4.0GHz Uncore, this means that we absolutely cannot achieve 2.0GHz memory and we can therefore not guarantee any stability for 2.0GHz memory. Technically, the maximum DRAM speed for a stable system is equal to (Max. Uncore) / (Safe QPI:Uncore Ratio) or 4.0GHz / 9:8 = 1.777GHz. In between 1.777GHz DRAM and 2.0GHz DRAM you are likely to experience some level of instability over the long term. Past 2.0GHz you are just plain lucky.

    2. Why is it that almost none of the X58 boards can reliably clock the BCLK over 222MHz?

    The answer to this again lies in the QPI link speed. At default (and lowest possible multiplier) for QPI of 18x the QPI link speed becomes 18x222MHz or 3.996GHz (4.0GHz). As we have already stated earlier this is dangerously close to the maximum QPI link speed and is therefore very unreliable. Anything higher than 222MHz and you have exceeded the current QPI maximum so in 99% of cases you will experience no POST. For this matter, a simple guideline is that any BCLK combined with a QPI multiplier that is at or very near maximum 4.0GHz QPI link speed is a candidate for no POST or instability.

    3. What the heck is the deal with the 20x multiplier then?

    This one is a real kicker (in a funny way). Yes, 20x multiplier is special, in more than one way, but mostly in the way people are trying to use it. You see, there is nothing wrong with the 20x multiplier. Indeed, it works, just like all other multipliers, perfectly fine. It is the DRAM multiplier and BCLK that people are combining with it that causes problems when combined with the QPI multiplier and the Uncore speed. At 20x200MHz, our default memory multiplier is 8 and our memory is at 1600MHz. The Uncore speed becomes 16x200MHz or 3.2GHz (or 2xDRAM at minimum). Therefore, remembering our (safe) ratios of 8:9 Uncore to QPI we see that the QPI link speed must be a minimum of 3.6GHz or higher. In case of 20x200MHz the Uncore and QPI are exactly in this ratio and with the added stress on the core, cache, IMC, DRAM, etc. this becomes a problem. At this point clock oscillations become much more prominent and if the QPI link speed falls below the 9:8 ratio to Uncore at any point in time combined with the added stress on the components the system can and likely will become unstable. Hence, at 20x200MHz with a default memory, Uncore and QPI multipliers we cannot really have a 100% stable system. So you say "just up the QPI link speed then". Not so fast. Remember our multipliers for QPI? They start at 18x, and the next is 22x, and so on. Unfortunately, 22x200MHz results in QPI link speed of 4.4GHz which results in no POST. Therefore, this cannot be done. Indeed, the highest reliable BCLK for default multipliers when using 20x core multiplier is 181MHz which with a 22x QPI multiplier would result in 3.982GHz QPI link. Even if you could set QPI multiplier to 20x, this would still not work for 99% of the boards out there as your QPI link would still be 4.0GHz. So what is the solution you ask? Memory multiplier. It needs to be lower. 1600MHz DRAM is approaching the maximum stress point for 20x200MHz core settings as it pushes on the limits of Uncore and QPI too much. By using a lower memory multiplier (say 6x if possible) the DRAM speed would become 6x200MHz or 1200MHz, Uncore could then be set at 2.4GHz with a lower multiplier which would then allow the QPI link to stay at 18x and well below the QPI link limits but still in a stable ratio to the Uncore.

    So there you go. A couple of answers to some of the most painful Core i7 questions. Unfortunately, if you can read between the lines, this does not bode well for anyone owning a Core i7 940 or a 965 EE. For all intents and purposes Core i7 920 performance and Core i7 940 performance are identical. Core i7 965 EE has more flexibility but only because of its unlocked multiplier which allows it to use lower BCLK speeds and DRAM multipliers to achieve higher clocks. Otherwise, it is no different than a Core i7 920 or a Core i7 940. Like I said before, this may also be a chipset imposed limitation, and the processors themselves may be a lot better but at the moment, the state of the affairs is like this.

    I have put a lot of thought and work into this so please if you want to comment do it constructively. I welcome any feedback and I hope that this will help a lot of people. It has helped me now to have a rock solid 4-core/8-thread, full 64-bit instruction set 4GHz air-only overclock on the Core i7 940 combined with a nice 1800MHz on my Corsair Dominator triple-channel sticks while keeping all of the voltages within Intel's recommended settings (i.e., DRAM is below 1.65V, QPI/DRAM is below 1.4V, and Vcore is below 1.39V under 100% load).
    I would seriously ask you to marry me if you could make a Core i7 overclock calculator that takes into account all the factors and variables you described.

    I understand what you said, but it's just too much info for me to remember when sitting down at the BIOS, unless I have a printed copy of what you wrote on hand, a scratch sheet of paper and an algebraic function calculator such as the TI-34.
    Asus Rampage II Gene | Core i7 920 | 6*2GB Mushkin 998729 | BFG GTX280 OCX | Auzentech X-Fi Forte | Corsair VX550
    —Life is too short to be bound by the moral, ethical and legal constraints imposed on us by modern day society.

  3. #878
    Xtreme Member Nanobot's Avatar
    Join Date
    May 2004
    Location
    Montreal
    Posts
    307
    That's some excellent observations there dejanh.

    So what we need is lower QPI multis to really push Core i7 to it's full potential.

    I kinda miss the independent memory handling of nVIDIA chipsets.
    The limited multis of intel chipset(and i7's mem. controller) are somewhat frustrating.

    How you got your Corsair Dominators to 1800mhz baffles me; I cant even get an extra 50mhz out of my 1600MHZ kit.
    Asus P6T Deluxe, Core i7 920 @ 4.1ghz, Corsair Dominator Tri channel 1600Mhz
    Evga GTX285, Raptor 150GB, Corsair HX620

    Apogee GTZ, PA 120.3, CM Stacker STC-01, DDC 3.1 MCP355/XSPC top.
    Win Vista Premium X64

  4. #879
    Xtreme Addict dejanh's Avatar
    Join Date
    May 2008
    Location
    Vancouver, BC, Canada
    Posts
    1,418
    Quote Originally Posted by 003 View Post
    I would seriously ask you to marry me if you could make a Core i7 overclock calculator that takes into account all the factors and variables you described.

    I understand what you said, but it's just too much info for me to remember when sitting down at the BIOS, unless I have a printed copy of what you wrote on hand, a scratch sheet of paper and an algebraic function calculator such as the TI-34.
    Hehe, I can try but I do not have access to all the chips and a few boards. I only had access to the non-extreme parts and a R2E board (mine). I would need to know all of the multipliers that are available for all chips and boards to make it a trully reliable calculator.

    In the meantime, you can also see what will be fixed in the next stepping of Core i7 here - http://download.intel.com/design/pro...pdt/320836.pdf

    Nothing that will improve overclocking though...

    Quote Originally Posted by Nanobot View Post
    That's some excellent observations there dejanh.

    So what we need is lower QPI multis to really push Core i7 to it's full potential.

    I kinda miss the independent memory handling of nVIDIA chipsets.
    The limited multis of intel chipset(and i7's mem. controller) are somewhat frustrating.

    How you got your Corsair Dominators to 1800mhz baffles me; I cant even get an extra 50mhz out of my 1600MHZ kit.
    Yeah, lower QPI multipliers would really help. But ideally, whatever is imposing the QPI limit needs to be removed. I doubt it is the CPU itself. I'd be betting it is the X58 chipset.

    On the note of the Dominators, to get 1800MHz out of the Dominators I had to drop the BCLK to 180MHz, use a 22x muliplier for Core i7 940 (default), use a 10x multiplier for DRAM, set Uncore to 3.6GHz, and set QPI multiplier to 22x. This nets me 3.96GHz core (4.14GHz turbo), 1804MHz DRAM, 3.6GHz Uncore, 3.96GHz QPI all on healthy voltages and air. My ratio of QPI to Uncore is sitting at 3.96:3.6 or 1.1 which is not ideal but likely stable enough for long term use without any noticable glitches.

    I am keeping turbo off now however, as I do not like its unpredictability.

    Here is a screenshot showing BIOS voltage settings. Particularly interesting is the QPI/DRAM as it is right in line with Intel's data sheet that specifies the maximum QPI/DRAM voltage for non-failure conditions. I measured them with a MM however directly on the board and they fall a bit below what is stated here (about 0.02V - 0.03V less). Better cooling and a cooler room (21C ambient) would also yield lower voltages for me, but hey, cheap and chic Also, I could do 181 BCLK to just get that every bit extra, but I like round numbers haha
    Attached Images Attached Images
    Last edited by dejanh; 12-12-2008 at 03:26 PM.

  5. #880
    Xtreme Member Classic Satch's Avatar
    Join Date
    Mar 2006
    Location
    Wasilla, AK
    Posts
    118
    Outstanding post dejanh!

    For curiosities sake, as I'm well aware that everybody's system is different, what are the settings that you are using to achieve your 4.0Ghz?
    Core i7 920@4.0Ghz(1.26v) - 6GB Corsair DDR3 1600 - WD Velociraptor 300GB - Asus P6T Deluxe - 2xEVGA GTX 260 216 Superclocked - Dell 2407WFP - Silverstone DA850 - Coolermaster Stacker 810

  6. #881
    I am Xtreme Hornet331's Avatar
    Join Date
    Jul 2007
    Location
    Austria
    Posts
    5,464
    Quote Originally Posted by Nanobot View Post
    That's some excellent observations there dejanh.

    So what we need is lower QPI multis to really push Core i7 to it's full potential.

    I kinda miss the independent memory handling of nVIDIA chipsets.
    The limited multis of intel chipset(and i7's mem. controller) are somewhat frustrating.
    Thats what you get from a IMC.

    Quote Originally Posted by dejanh View Post
    Hehe, I can try but I do not have access to all the chips and a few boards. I only had access to the non-extreme parts and a R2E board (mine). I would need to know all of the multipliers that are available for all chips and boards to make it a trully reliable calculator.

    In the meantime, you can also see what will be fixed in the next stepping of Core i7 here - http://download.intel.com/design/pro...pdt/320836.pdf

    Nothing that will improve overclocking though...



    Yeah, lower QPI multipliers would really help. But ideally, whatever is imposing the QPI limit needs to be removed. I doubt it is the CPU itself. I'd be betting it is the X58 chipset.

    On the note of the Dominators, to get 1800MHz out of the Dominators I had to drop the BCLK to 180MHz, use a 22x muliplier for Core i7 940 (default), use a 10x multiplier for DRAM, set Uncore to 3.6GHz, and set QPI multiplier to 22x. This nets me 3.96GHz core (4.14GHz turbo), 1804MHz DRAM, 3.6GHz Uncore, 3.96GHz QPI all on healthy voltages and air. My ratio of QPI to Uncore is sitting at 3.96:3.6 or 1.1 which is stable enough for long term use.

    I am keeping turbo off now however, as I do not like its unpredictability.
    You just could make a quick and diry excel sheet.

  7. #882
    Xtreme Member bmilos's Avatar
    Join Date
    Dec 2008
    Location
    Hollywoooooood, CA
    Posts
    238
    Where exactly do you set the QPI multiplier?

    Thanks for all your work.


    i7 965 | Rampage 2 Extreme | Asus 4870X2 | 6gb OCZ BLADE 7-8-7-20 | 4 OCZ SSD V2 in RAID0 |
    1 VelociRaptor 300gb | 1 WD Caviar Black 1TB | Tagan ITZ 1100w PSU | LG 6x BluRay Burner | 52" Sony Bravia LCD

    Homemade SS Phase Change | Kayl Custom Lineset

    My Case - Treasure Chest Build Thread : http://www.xtremesystems.org/forums/...d.php?t=218115

  8. #883
    I am Xtreme safan80's Avatar
    Join Date
    Oct 2004
    Location
    U.S.A.
    Posts
    4,743
    Quote Originally Posted by dejanh View Post
    So there you go. A couple of answers to some of the most painful Core i7 questions. Unfortunately, if you can read between the lines, this does not bode well for anyone owning a Core i7 940 or a 965 EE. For all intents and purposes Core i7 920 performance and Core i7 940 performance are identical. Core i7 965 EE has more flexibility but only because of its unlocked multiplier which allows it to use lower BCLK speeds and DRAM multipliers to achieve higher clocks. Otherwise, it is no different than a Core i7 920 or a Core i7 940. Like I said before, this may also be a chipset imposed limitation, and the processors themselves may be a lot better but at the moment, the state of the affairs is like this.

    I have put a lot of thought and work into this so please if you want to comment do it constructively. I welcome any feedback and I hope that this will help a lot of people. It has helped me now to have a rock solid 4-core/8-thread, full 64-bit instruction set 4GHz air-only overclock on the Core i7 940 combined with a nice 1800MHz on my Corsair Dominator triple-channel sticks while keeping all of the voltages within Intel's recommended settings (i.e., DRAM is below 1.65V, QPI/DRAM is below 1.4V, and Vcore is below 1.39V under 100% load).
    I take it that your only running 3 sticks? I've got 20x189 using the 2:8 mem multi with 6 sticks stable using the same voltages as the prime I posted. I believe there's no difference between the 920, 940, 965 XE chips other than the multis. Evga released a beta bios that unlocked the other memory multis for the non XE chips.


    Asus Z9PE-D8 WS with 64GB of registered ECC ram.|Dell 30" LCD 3008wfp:7970 video card

    LSI series raid controller
    SSDs: Crucial C300 256GB
    Standard drives: Seagate ST32000641AS & WD 1TB black
    OSes: Linux and Windows x64

  9. #884
    Xtreme Addict rge's Avatar
    Join Date
    Jun 2007
    Posts
    1,420
    interesting observations, mine may just be an exception...
    my 20x200 run prime stable 9hrs...
    Vtt 1.32, uncore 18x, QPI 36x, mem 8x
    vcore 1.33 load, 1.356 bios
    ram 1600mhz
    Attached Images Attached Images
    Last edited by rge; 12-12-2008 at 03:46 PM.
    3770K 4.7 w/1.31 - UD5 z77 - Dom 1866 - Corsair HX850 - Intel 520 240gb - GTX 680 - 26 inch Samsung LCD
    xspc 360 + SR1 280 + HC 680 + EK sup hiflo
    Lian Li A71F

  10. #885
    Xtreme Member Bootsy's Avatar
    Join Date
    Jun 2005
    Location
    The MotherShip
    Posts
    456
    Quote Originally Posted by Bobbylite View Post
    bootsy what is you WC setup, nice work
    Quote Originally Posted by bmilos View Post
    @Bootsy - what are your other settings? I am running at the same 200x21 @ 1.43750 on a GTZ too, and my load temp is about 88c. Is the CPU the only block in your loop? I also have my NB in my loop. Maybe thats the root?
    I only have the cpu block in my loop running a Pa 120.3 with Petra's Yate L oons and some no name red led fans in a push-pull config. I am priming at 4320 with 1.48 volts now temps still good at idle and load.
    Attached Images Attached Images
    "Behold, I am Funkadelic. I am not of your world. But fear me not, I will do you no harm. Loan me your funky mind and I shall play with it. For nothing is good unless you play with it. And all that is good, is nasty!"
    ("What Is Soul," Funkadelic, 1969)


  11. #886
    Xtreme Addict dejanh's Avatar
    Join Date
    May 2008
    Location
    Vancouver, BC, Canada
    Posts
    1,418
    Quote Originally Posted by bmilos View Post
    Where exactly do you set the QPI multiplier?

    Thanks for all your work.
    It's known as QPI link data rate I think on R2E (speaking from memory). You have to work out the multiplier backwards from the MT/s figure. So if you have a 7200MT/s, that translates to 3.6GHz which with a 200MHz BCLK translates to 18x QPI multiplier.

  12. #887
    I am Xtreme Hornet331's Avatar
    Join Date
    Jul 2007
    Location
    Austria
    Posts
    5,464
    Quote Originally Posted by dejanh View Post
    It's known as QPI link data rate I think on R2E (speaking from memory). You have to work out the multiplier backwards from the MT/s figure. So if you have a 7200MT/s, that translates to 3.6GHz which with a 200MHz BCLK translates to 18x QPI multiplier.
    Gigabyte takes GT/s as reference so they have a 36/40/44 multi, Asus on the other hand takes the actual clock so its multi 18/20/22.

    Just stay under 8000GT/s / 4000MHz qpi clock and thing should be fine.

  13. #888
    Xtreme Member
    Join Date
    Sep 2008
    Posts
    270
    Quote Originally Posted by dejanh View Post
    Ok, I think I finally have some answers to the 20x multiplier instability and a number of other issues many users are complaining about. You will have to follow me here as this is not that simple, but it makes a lot of sense and all of my testing to date has actually confirmed it. I have spent a lot of time figuring this out and I really hope that this will help people. Indeed, I am now able to predict ahead of time what settings will POST, what settings will not, and approximately which component will need to be juiced up higher to result in a more stable system. Furthermore, this will be a very thorough overview of Core i7 overclocking that will expose some serious limitations, particularly on the i7 920 and i7 940 parts. It is all primarily linked to the Uncore and QPI speeds.
    First off, I will use the Core i7 940 for all of my examples. Core i7 920 and i7 940 are for all intents and purposes the exact same chip, but the i7 940 is just factory clocked higher. These are most likely not higher binned chips, and even if they are by some chance it really does not matter. You will soon see why. In essence, same holds true for the i7 965 EE though they are certainly higher binned and quite likely somewhat more forgiving when overclocking. The fact that they can overclock using an unlocked multiplier is a huge bonus for this chip.
    For details on each of the CPU specifications see Intel's website and tech specs/data sheets. I'll just briefly mention the specs here, for reference.

    Core i7 920 - 2.66GHz, 20x133MHz, 4.8GT/s QPI (2.4GHz), QPI multiplier 18x (18x133MHz)
    Core i7 940 - 2.93GHz, 22x133MHz, 4.8GT/s QPI (2.4GHz), QPI multiplier 18x (18x133MHz)
    Core i7 965 EE - 3.2GHz, 24x133MHz, 6.4GT/s QPI (3.2GHz), QPI multiplier 24x (24x133MHz)

    The key thing to remember here is that for Core i7 processors everything is interconnected, much like in case of AMD processors. Therefore, changing the BCLK speed affects everything from core speed, to QPI link speed, to Uncore speed, to memory speed. The key elements and the limiting ones here are the last three, the QPI link speed, Uncore speed, and memory speed. Particularly, the QPI is the limiting factor for the other elements as the highest stable QPI link speed for the current Core i7 processors is 8.0GT/s or 4.0GHz for 99% of systems out there. Some exceptions have been observed, but these are extremely rare. This may also be chipset dependent limitation and it is possible that newer chipsets supporting Core i7 will not have this limitation. Anyway, enough introduction. Let's get to the details.

    First let's look at the relationships between QPI, Uncore, and DRAM speeds.

    DRAM speed must be in a 1:2 ratio or less to Uncore speed which in turn must be in 1:1 or less ratio to QPI link speed (8:9 Uncore to QPI or lower is preferred as the more you approach 1:1 the more unstable the system becomes).

    Now that we know this relationship, let's dive right into some of the most common issues with Core i7 processors.

    1. Why is it that I cannot run my 2000MHz memory in my new Core i7 system?

    To understand this note the maximum QPI link speed we mentioned earlier. Using the simple ratio we defined, we can see that with the maximum QPI link speed of 4.0GHz we can have a theoretical maximum Uncore of 4.0GHz and a maximum memory speed of 2.0GHz. These however are only theoretical maximums and are by no means guaranteed. For starters, QPI and Uncore cannot be run at the same speed as any clock oscillations can result in a crash if the ratio of QPI to Uncore ever falls below 1:1. Therefore, Uncore must always be below QPI to avoid this, and preferably below the 8:9 Uncore to QPI ratio to guarantee stability. Consequently, if we cannot achieve 4.0GHz Uncore, this means that we absolutely cannot achieve 2.0GHz memory and we can therefore not guarantee any stability for 2.0GHz memory. Technically, the maximum DRAM speed for a stable system is equal to (Max. Uncore) / (Safe QPI:Uncore Ratio) or 4.0GHz / 9:8 = 1.777GHz. In between 1.777GHz DRAM and 2.0GHz DRAM you are likely to experience some level of instability over the long term. Past 2.0GHz you are just plain lucky.

    2. Why is it that almost none of the X58 boards can reliably clock the BCLK over 222MHz?

    The answer to this again lies in the QPI link speed. At default (and lowest possible multiplier) for QPI of 18x the QPI link speed becomes 18x222MHz or 3.996GHz (4.0GHz). As we have already stated earlier this is dangerously close to the maximum QPI link speed and is therefore very unreliable. Anything higher than 222MHz and you have exceeded the current QPI maximum so in 99% of cases you will experience no POST. For this matter, a simple guideline is that any BCLK combined with a QPI multiplier that is at or very near maximum 4.0GHz QPI link speed is a candidate for no POST or instability.

    3. What the heck is the deal with the 20x multiplier then?

    This one is a real kicker (in a funny way). Yes, 20x multiplier is special, in more than one way, but mostly in the way people are trying to use it. You see, there is nothing wrong with the 20x multiplier. Indeed, it works, just like all other multipliers, perfectly fine. It is the DRAM multiplier and BCLK that people are combining with it that causes problems when combined with the QPI multiplier and the Uncore speed. At 20x200MHz, our default memory multiplier is 8 and our memory is at 1600MHz. The Uncore speed becomes 16x200MHz or 3.2GHz (or 2xDRAM at minimum). Therefore, remembering our (safe) ratios of 8:9 Uncore to QPI we see that the QPI link speed must be a minimum of 3.6GHz or higher. In case of 20x200MHz the Uncore and QPI are exactly in this ratio and with the added stress on the core, cache, IMC, DRAM, etc. this becomes a problem. At this point clock oscillations become much more prominent and if the QPI link speed falls below the 9:8 ratio to Uncore at any point in time combined with the added stress on the components the system can and likely will become unstable. Hence, at 20x200MHz with a default memory, Uncore and QPI multipliers we cannot really have a 100% stable system. So you say "just up the QPI link speed then". Not so fast. Remember our multipliers for QPI? They start at 18x, and the next is 22x, and so on. Unfortunately, 22x200MHz results in QPI link speed of 4.4GHz which results in no POST. Therefore, this cannot be done. Indeed, the highest reliable BCLK for default multipliers when using 20x core multiplier is 181MHz which with a 22x QPI multiplier would result in 3.982GHz QPI link. Even if you could set QPI multiplier to 20x, this would still not work for 99% of the boards out there as your QPI link would still be 4.0GHz. So what is the solution you ask? Memory multiplier. It needs to be lower. 1600MHz DRAM is approaching the maximum stress point for 20x200MHz core settings as it pushes on the limits of Uncore and QPI too much. By using a lower memory multiplier (say 6x if possible) the DRAM speed would become 6x200MHz or 1200MHz, Uncore could then be set at 2.4GHz with a lower multiplier which would then allow the QPI link to stay at 18x and well below the QPI link limits but still in a stable ratio to the Uncore.

    So there you go. A couple of answers to some of the most painful Core i7 questions. Unfortunately, if you can read between the lines, this does not bode well for anyone owning a Core i7 940 or a 965 EE. For all intents and purposes Core i7 920 performance and Core i7 940 performance are identical. Core i7 965 EE has more flexibility but only because of its unlocked multiplier which allows it to use lower BCLK speeds and DRAM multipliers to achieve higher clocks. Otherwise, it is no different than a Core i7 920 or a Core i7 940. Like I said before, this may also be a chipset imposed limitation, and the processors themselves may be a lot better but at the moment, the state of the affairs is like this.

    I have put a lot of thought and work into this so please if you want to comment do it constructively. I welcome any feedback and I hope that this will help a lot of people. It has helped me now to have a rock solid 4-core/8-thread, full 64-bit instruction set 4GHz air-only overclock on the Core i7 940 combined with a nice 1800MHz on my Corsair Dominator triple-channel sticks while keeping all of the voltages within Intel's recommended settings (i.e., DRAM is below 1.65V, QPI/DRAM is below 1.4V, and Vcore is below 1.39V under 100% load).
    200 x 21 is still priming, it's only been 25 minutes, but normally it crashes in like 1-2 minutes, so this is a good sign.
    Last edited by Lukee; 12-12-2008 at 06:14 PM.

  14. #889
    Xtreme Addict fornowagain's Avatar
    Join Date
    Nov 2005
    Location
    UK
    Posts
    1,074
    Quote Originally Posted by Hornet331 View Post
    Gigabyte takes GT/s as reference so they have a 36/40/44 multi,
    Mines 36/44/48?

    Quote Originally Posted by dejanh View Post
    DRAM speed must be in a 1:2 ratio or less to Uncore speed which in turn must be in 1:1 or less ratio to QPI link speed (8:9 Uncore to QPI or lower is preferred as the more you approach 1:1 the more unstable the system becomes).
    Can I ask where the 8:9 ratio comes from?

    Quote Originally Posted by Lukee View Post
    Ok, so that means for me running memory 8x uncore 16x and QPI 36x what do I have the change to get 200 x 21 stable?
    From this..



    Going by that, by dropping the mem multi along with uncore. Although you could push it to x15 and stay under the described ratio.

    Last edited by fornowagain; 12-12-2008 at 06:32 PM.

    i7| EX58-EXTREME | SSD M225 | Radbox | 5870CF + 9600GT

  15. #890
    Xtreme Member
    Join Date
    Sep 2008
    Posts
    270
    Quote Originally Posted by fornowagain View Post
    Mines 36/44/48?

    Can I ask where the 8:9 ratio comes from?


    From this..



    Going by that, by dropping the mem multi along with uncore. Although you could push it to x15 and stay under the described ratio.

    Thanks. Just reinstalled Office and created a spreadsheet like yours.

    Why won't they give us a QPI multiplier of 40? That would solve things.

    40x 16x 8x and we are good to go. On that same note, are they going to open up odd numbered multipliers for memory? It sucks that at 200 Bclk, you only have 1200 - 1600 - 2000 to choose from.

    Do you forsee the new bios updates giving us more values so we have more control over the OCs?

  16. #891
    Registered User D3mon_Hunt3r's Avatar
    Join Date
    Nov 2004
    Location
    Portugal, Porto
    Posts
    61
    Congrats dejanh best enlightning post i have seen in weeks!
    H5N1 Online Dual Lian Li V2000B WC Triple Loop active
    i7 920 B Apogee GTZ/ DFI UT X58-T3eH8 Mips Coldzero WC/ Corsair 6Gb DDR3 w/ 2x Silenx 80mm 14dBA 32CFM Custom Coldzero Cooler
    HDA Xplosion @ DTT3500 DDL / Corsair HX1000W / Powercolor 4870X2 @ Dell 2408WFP + 2407WFP-HC
    5.6Tb (2x VelociRaptor300 RAID0, + 2x Seagate1.5Tb + 1 x Seagate1Tb + 1x Sam1Tb) w/2x Silentstar Quad Rev2
    Lazy OC'er Audio Upgrade Next Feedback Techzone

  17. #892
    Xtreme Enthusiast sonofander's Avatar
    Join Date
    Jan 2007
    Location
    Los Angeles, CA
    Posts
    628
    Quote Originally Posted by Bootsy View Post
    I only have the cpu block in my loop running a Pa 120.3 with Petra's Yate L oons and some no name red led fans in a push-pull config. I am priming at 4320 with 1.48 volts now temps still good at idle and load.

    What speed are you running your memory?
    Are you still priming?
    Very interested in a stable 4.3 oc
    2600k @ 5ghz / z68 Pro / 8gb Ripjaws X / GTX 580 SLi
    2x Inferno raid 0 / WD 1TB Black / Thermaltake 1200w
    Dell 3008 WFP / Dual Loop WC MM UFO

  18. #893
    Xtreme Member
    Join Date
    Sep 2008
    Posts
    270
    I finally have 200x21 stable, @ 1.44v(bios), 1.404 CPUz

    Funny thing is that my 195 x 21 was stable with 1.35v(bios) AND I can run my memory at 1600 not 1200.

    For that extra 105 Mhz, it's costing me 2000 MB/s in Read memory and almost a full .1 more in Vcore. I don't think it's worth it at the present time. What do you guys think?

  19. #894
    Xtreme Addict dejanh's Avatar
    Join Date
    May 2008
    Location
    Vancouver, BC, Canada
    Posts
    1,418
    Quote Originally Posted by safan80 View Post
    I take it that your only running 3 sticks? I've got 20x189 using the 2:8 mem multi with 6 sticks stable using the same voltages as the prime I posted. I believe there's no difference between the 920, 940, 965 XE chips other than the multis. Evga released a beta bios that unlocked the other memory multis for the non XE chips.
    Yeah, only 3 sticks. 6 should work as well however.
    Last edited by dejanh; 12-13-2008 at 09:32 AM.

  20. #895
    I am Xtreme Hornet331's Avatar
    Join Date
    Jul 2007
    Location
    Austria
    Posts
    5,464
    Quote Originally Posted by fornowagain View Post
    Mines 36/44/48?
    ops, sry i had the wrong numbers in my mind.

  21. #896
    Xtreme Addict Xello's Avatar
    Join Date
    Mar 2008
    Location
    UK
    Posts
    1,075
    On my GB board my lowest QPI multi is 36x, other than 'slow mode' which brings the QPI clock to sub-100mhz range. When i choose 36x though i am clearly on 18x because my QPI clock shows as 3.9ghz rather than 7.8ghz.
    TJ07 | Corsair HX1000W | Gigabyte EX58 Extreme | i7 950 @ 4.4ghz | Ek Supreme | Thermochill PA 120.3 | Laing DDC 12v w/ mod plexi top | 3x2gb Corsair XMS3 1600mhz | GTX 580 | Raid 0 300gb Velociraptor x 2 | Razer Lachesis & Lycosa | Win7 HP x64 | fluffy dice.

  22. #897
    Xtreme Addict rge's Avatar
    Join Date
    Jun 2007
    Posts
    1,420
    Anyone find raising the IOH core..input/output hub... volts on cpu, has any effect on stable overclocks especially at higher bclk? Was reading last night somewhere, and on one thread on this forum that some were increasing it to get higher bclk? I have not played with it much yet, but I think I had it raised on my 20x200 run, but thought it irrelevant after rerunning my 182x22 run still stable with normal IOH, now not sure if that setting matters or not. Going to play with it on my current settings to see if can lower vcore. Or does anyone have explanation of what it does...all I know it is on cpu, IOH is interconnected via qpi to cpu, and IOH connects to ? pci peripherals?
    3770K 4.7 w/1.31 - UD5 z77 - Dom 1866 - Corsair HX850 - Intel 520 240gb - GTX 680 - 26 inch Samsung LCD
    xspc 360 + SR1 280 + HC 680 + EK sup hiflo
    Lian Li A71F

  23. #898
    Registered User
    Join Date
    Mar 2005
    Location
    Michigan
    Posts
    57

    4.2 6hrs prime stable ht off

    Volts required to get to 4.2 6hrs prime (blend)= 1.38 and cpu pll to 1.86 all others auto. Haven't pushed her further yet.
    Water cooled with 120.3 ambient temp=49F (Michigan basement).
    Attached Images Attached Images
    Main machine
    i7-920
    P6T Deluxe
    4870x2
    6gig Gskill
    corsair 1000w

    Rig#2:
    E6700 @3.5 1.45volts
    P5W DH Deluxe
    2x1gig Crucial Ballistic 6400 @438mhz 4.4.4.4/2.3volts
    hd2900xt
    2x74gig raptor's in raid 0
    700watt Zippy

  24. #899
    Xtreme Addict HKPolice's Avatar
    Join Date
    Mar 2004
    Location
    Toronto, Ontario Canada
    Posts
    1,436
    Quote Originally Posted by dejanh View Post
    Ok, I think I finally have some answers to the 20x multiplier instability and a number of other issues many users are complaining about. You will have to follow me here as this is not that simple, but it makes a lot of sense and all of my testing to date has actually confirmed it. I have spent a lot of time figuring this out and I really hope that this will help people. Indeed, I am now able to predict ahead of time what settings will POST, what settings will not, and approximately which component will need to be juiced up higher to result in a more stable system. Furthermore, this will be a very thorough overview of Core i7 overclocking that will expose some serious limitations, particularly on the i7 920 and i7 940 parts. It is all primarily linked to the Uncore and QPI speeds.
    First off, I will use the Core i7 940 for all of my examples. Core i7 920 and i7 940 are for all intents and purposes the exact same chip, but the i7 940 is just factory clocked higher. These are most likely not higher binned chips, and even if they are by some chance it really does not matter. You will soon see why. In essence, same holds true for the i7 965 EE though they are certainly higher binned and quite likely somewhat more forgiving when overclocking. The fact that they can overclock using an unlocked multiplier is a huge bonus for this chip.
    For details on each of the CPU specifications see Intel's website and tech specs/data sheets. I'll just briefly mention the specs here, for reference.

    Core i7 920 - 2.66GHz, 20x133MHz, 4.8GT/s QPI (2.4GHz), QPI multiplier 18x (18x133MHz)
    Core i7 940 - 2.93GHz, 22x133MHz, 4.8GT/s QPI (2.4GHz), QPI multiplier 18x (18x133MHz)
    Core i7 965 EE - 3.2GHz, 24x133MHz, 6.4GT/s QPI (3.2GHz), QPI multiplier 24x (24x133MHz)

    The key thing to remember here is that for Core i7 processors everything is interconnected, much like in case of AMD processors. Therefore, changing the BCLK speed affects everything from core speed, to QPI link speed, to Uncore speed, to memory speed. The key elements and the limiting ones here are the last three, the QPI link speed, Uncore speed, and memory speed. Particularly, the QPI is the limiting factor for the other elements as the highest stable QPI link speed for the current Core i7 processors is 8.0GT/s or 4.0GHz for 99% of systems out there. Some exceptions have been observed, but these are extremely rare. This may also be chipset dependent limitation and it is possible that newer chipsets supporting Core i7 will not have this limitation. Anyway, enough introduction. Let's get to the details.

    First let's look at the relationships between QPI, Uncore, and DRAM speeds.

    DRAM speed must be in a 1:2 ratio or less to Uncore speed which in turn must be in 1:1 or less ratio to QPI link speed (8:9 Uncore to QPI or lower is preferred as the more you approach 1:1 the more unstable the system becomes).

    Now that we know this relationship, let's dive right into some of the most common issues with Core i7 processors.

    1. Why is it that I cannot run my 2000MHz memory in my new Core i7 system?

    To understand this note the maximum QPI link speed we mentioned earlier. Using the simple ratio we defined, we can see that with the maximum QPI link speed of 4.0GHz we can have a theoretical maximum Uncore of 4.0GHz and a maximum memory speed of 2.0GHz. These however are only theoretical maximums and are by no means guaranteed. For starters, QPI and Uncore cannot be run at the same speed as any clock oscillations can result in a crash if the ratio of QPI to Uncore ever falls below 1:1. Therefore, Uncore must always be below QPI to avoid this, and preferably below the 8:9 Uncore to QPI ratio to guarantee stability. Consequently, if we cannot achieve 4.0GHz Uncore, this means that we absolutely cannot achieve 2.0GHz memory and we can therefore not guarantee any stability for 2.0GHz memory. Technically, the maximum DRAM speed for a stable system is equal to (Max. Uncore) / (Safe QPI:Uncore Ratio) or 4.0GHz / 9:8 = 1.777GHz. In between 1.777GHz DRAM and 2.0GHz DRAM you are likely to experience some level of instability over the long term. Past 2.0GHz you are just plain lucky.

    2. Why is it that almost none of the X58 boards can reliably clock the BCLK over 222MHz?

    The answer to this again lies in the QPI link speed. At default (and lowest possible multiplier) for QPI of 18x the QPI link speed becomes 18x222MHz or 3.996GHz (4.0GHz). As we have already stated earlier this is dangerously close to the maximum QPI link speed and is therefore very unreliable. Anything higher than 222MHz and you have exceeded the current QPI maximum so in 99% of cases you will experience no POST. For this matter, a simple guideline is that any BCLK combined with a QPI multiplier that is at or very near maximum 4.0GHz QPI link speed is a candidate for no POST or instability.

    3. What the heck is the deal with the 20x multiplier then?

    This one is a real kicker (in a funny way). Yes, 20x multiplier is special, in more than one way, but mostly in the way people are trying to use it. You see, there is nothing wrong with the 20x multiplier. Indeed, it works, just like all other multipliers, perfectly fine. It is the DRAM multiplier and BCLK that people are combining with it that causes problems when combined with the QPI multiplier and the Uncore speed. At 20x200MHz, our default memory multiplier is 8 and our memory is at 1600MHz. The Uncore speed becomes 16x200MHz or 3.2GHz (or 2xDRAM at minimum). Therefore, remembering our (safe) ratios of 8:9 Uncore to QPI we see that the QPI link speed must be a minimum of 3.6GHz or higher. In case of 20x200MHz the Uncore and QPI are exactly in this ratio and with the added stress on the core, cache, IMC, DRAM, etc. this becomes a problem. At this point clock oscillations become much more prominent and if the QPI link speed falls below the 9:8 ratio to Uncore at any point in time combined with the added stress on the components the system can and likely will become unstable. Hence, at 20x200MHz with a default memory, Uncore and QPI multipliers we cannot really have a 100% stable system. So you say "just up the QPI link speed then". Not so fast. Remember our multipliers for QPI? They start at 18x, and the next is 22x, and so on. Unfortunately, 22x200MHz results in QPI link speed of 4.4GHz which results in no POST. Therefore, this cannot be done. Indeed, the highest reliable BCLK for default multipliers when using 20x core multiplier is 181MHz which with a 22x QPI multiplier would result in 3.982GHz QPI link. Even if you could set QPI multiplier to 20x, this would still not work for 99% of the boards out there as your QPI link would still be 4.0GHz. So what is the solution you ask? Memory multiplier. It needs to be lower. 1600MHz DRAM is approaching the maximum stress point for 20x200MHz core settings as it pushes on the limits of Uncore and QPI too much. By using a lower memory multiplier (say 6x if possible) the DRAM speed would become 6x200MHz or 1200MHz, Uncore could then be set at 2.4GHz with a lower multiplier which would then allow the QPI link to stay at 18x and well below the QPI link limits but still in a stable ratio to the Uncore.

    So there you go. A couple of answers to some of the most painful Core i7 questions. Unfortunately, if you can read between the lines, this does not bode well for anyone owning a Core i7 940 or a 965 EE. For all intents and purposes Core i7 920 performance and Core i7 940 performance are identical. Core i7 965 EE has more flexibility but only because of its unlocked multiplier which allows it to use lower BCLK speeds and DRAM multipliers to achieve higher clocks. Otherwise, it is no different than a Core i7 920 or a Core i7 940. Like I said before, this may also be a chipset imposed limitation, and the processors themselves may be a lot better but at the moment, the state of the affairs is like this.

    I have put a lot of thought and work into this so please if you want to comment do it constructively. I welcome any feedback and I hope that this will help a lot of people. It has helped me now to have a rock solid 4-core/8-thread, full 64-bit instruction set 4GHz air-only overclock on the Core i7 940 combined with a nice 1800MHz on my Corsair Dominator triple-channel sticks while keeping all of the voltages within Intel's recommended settings (i.e., DRAM is below 1.65V, QPI/DRAM is below 1.4V, and Vcore is below 1.39V under 100% load).
    Please explain how this is possible then: http://www.xtremesystems.org/forums/...79&postcount=2

    2Ghz Ram, 4Ghz Uncore but only 2.5ghz QDI speed with 143Mhz BCLK x18 QDI multiplier.

    Has anyone else confirmed that QDI has to be faster than Uncore to POST?

  25. #900
    Xtreme Addict rge's Avatar
    Join Date
    Jun 2007
    Posts
    1,420
    Quote Originally Posted by HKPolice View Post

    Has anyone else confirmed that QDI has to be faster than Uncore to POST?
    Some prime runs on mine have uncore faster than QPI link speed...I am running with uncore faster than QPI now.
    Attached Images Attached Images
    3770K 4.7 w/1.31 - UD5 z77 - Dom 1866 - Corsair HX850 - Intel 520 240gb - GTX 680 - 26 inch Samsung LCD
    xspc 360 + SR1 280 + HC 680 + EK sup hiflo
    Lian Li A71F

Page 36 of 138 FirstFirst ... 26333435363738394686136 ... LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •