Beware of VTT - it's a lurking time bomb...
by Gary Key on April 16, 2008 12:00 AM EST- Posted in
- Gary's First Looks
High VTT sends our best QX9650 to an early grave...
We have been using this particular QX960 processor for an upcoming X48 comparison article and testing was going quite well (not blaming a particular board somehow seems appropriate). We thought we had made it past that mystical, magical, and more importantly, stable mark of 450FSB with a Quad Core. However, in order to get to that point on this particular board, we (Editor- Raja in case the police get involved) made the mistake of using a very high VTT termination voltage of 1.51V (VTT is used to terminate data lines between the MCH and CPU).
We should have known better really, especially after Kris posted up a recommended voltage-operating chart in the ASUS Striker II Extreme review. We do not know what is worse now, Kris saying I told you so (jokingly, well maybe not) or the thought of replacing this $1000 CPU. We thought it would be beneficial for others to learn from our mistakes so here goes.
This particular CPU was a great example of a QX9650 hitting 4GHz stable at a mere 1.29V on most motherboards (tears are flowing in the beer tonight). We know users are running VTT voltages even higher than ours on 45nm processors and probably have not had a problem yet. We will run high VTT voltages in short bursts to test the limits of the board and CPU. However, this is the first time we have tried anything over 1.45V on a 24+-hour basis to test application stability.
Let this be a warning – do not go over 1.4V maximum for 24/7 use! We are certain that the high VTT voltage and extended testing was the cause of death, as we made no other major or obvious changes within the BIOS that could have instigated a failure. Obviously, we tried to boot the processor in a number of other motherboards without success before we decided to post our results up.
This is our first 45nm Quad core processor we managed to kill outright during testing. We hope it is the last one too. The problem is that we also have a Q9300 that is on life support after experiencing a 36-hour run at 435FSB with VTT set to 1.45V. While our experiences might not represent results elsewhere, we thought our advice to just, “Say no to high VTT” is worth a quick post. We have had enough VTT/GTL adjusting in the last year to last us a lifetime – just give us Nehalem quickly, please.
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autumnale - Tuesday, May 6, 2008 - link
http://www.intel.com/design/processor/datashts/318...">http://www.intel.com/design/processor/datashts/318...http://download.intel.com/design/processor/datasht...">http://download.intel.com/design/processor/datasht...
On page 19, Table 2-2 says that the absolute maximum for the FSB termination voltage is... 1.45V
But I think y'all know that by now I think. :)
And section 2.6.1 states... And I quote:
"At conditions exceeding absolute maximum and minimum ratings, neither functionality nor long-term reliability can be expected. Moreover, if a device is subjected to these conditions for any length of time then, when returned to conditions within the functional operating condition limits, it will either not function, or its reliability will be severely degraded."
I should stop rubbing salt into wounds really. :) I'm just kidding. Seriously, someone had to make the mistake of frying a $1000 CPU so the rest of us won't make the same mistake right?
sirokket16 - Sunday, April 20, 2008 - link
Can you please do more testing before you make a post like this? I am very skeptical of your "empirical" findings and I'm sure many others are too. I have been running max Vtt on my board (1.55v) since I bought my processor last summer and I have had zero problems. I think saying things like this creates a false scare within the overclocking community. Many others have been running high Vtts without issue. Not once have I heard this from anyone. Please update your "empirical" findings with some more hard evidence.Heyres - Monday, May 5, 2008 - link
Can't agree more... I really enjoy reading what you guys have to say, but I think a 1,4V is a really low VTT... I don't think the everyday use can be compared to a 24h stress test. If I use it to reduce a bottele neck on a game for exemple, when the CPU isn't 100% load for more that a few minutes (surely much less than that), can it be that dangerous? What a joy it would be to see some mores facts to backup that information... well maybe when I get a lil richer ill do that my self... till then ill listen what u guys have to say... =)royalcrown - Sunday, April 20, 2008 - link
While it does suck... I really don't feel sorry for most over clockers that do this....they'll go and spend 4 to 6 hundred dollars on water cooling crap and buy a cheap cpu when they could've just bought the next few steps up most of the time ! When there is no next step up...we'll it might just be better to have patience....lol.All the money people saved by ocing is wiped out when they have to buy uber expensive ram, 300 dollar motherboards and replace their marshmallow of a cpu.
Syzygies - Thursday, April 17, 2008 - link
While I fully intend to follow this advice (it coincided with a near disaster playing with a Q6600), I wonder while reading the words "most motherboards":Intel actually specs a frighteningly small number of reseatings for a cpu. How do you play hard with a cpu without going over this count, and what are the consequences?
(My very first build, I snagged the 775 "bed of copper grass" with an anti-static glove, and spent the next hour with a magnifying glass grooming the bed of grass. That's one Q6600 I plan to never reseat!)
kjboughton - Wednesday, April 16, 2008 - link
For those that are requesting proof that excessive VTT was the cause of the failure, just know that our conclusions are based more on empirical evidence than anything else; however, we have had more than one conversation with Intel CPU power engineers regarding the practical limit of VTT. In general, Intel does an excellent job of providing a wide selection of both technical and educational documents available for download by anyone directly from their website. Oftentimes significant technical insight can be gained by merely taking a few moments to read through some of these publications. As an example, anyone wishing to know more about the 45nm voltage constraints as recommend by Intel can find more information here – http://download.intel.com/design/processor/datasht...">http://download.intel.com/design/processor/datasht...Intel® Core™2 Extreme Processor QX9000 Series and Intel® Core™2 Quad Processor Q9000 Series Datasheet (Document Number: 318726-003) was first published in March 2008. Section 2, Electrical Specifications, Subsection 2.6, Voltage and Current Specifications, Table 2-2, titled Absolute Minimum and Maximum Ratings, specifies absolute maximum and minimum ratings for this series of processors. It’s important to note that these values lie outside the functional limits of these processors (i.e. they may not be indicative of warranted operating voltages but are rather intended to serve as warning to those that would run their processors above rated specifications).
Table 2-2 shows maximum voltages for both VTT (FSB Termination Voltage) and VCC (Vcore) with respect to VSS (the processor power ground plane voltage, a.k.a. “ground”). In this case they happen to be equal in magnitude – 1.45V. If anything, this suggests that the use of high VTT voltages can be potentially as damaging, if not more so, than the sustained application of Vcore voltages above this same voltage yet many users continue to operate under the assumption that excessive VTT voltages should be less concerning than higher Vcore voltages.
The attitude that only Vcore can damage a CPU is one that has prevailed for far too long. Many users where initially “shocked” to learn that high PLL voltages (used to provide power to the complex array of circuits used to distribute the CPU’s common clocking signal) could permanently damage or cripple a CPU with little or no advanced warning. Even today there are those that outwardly deny the possibility of failure due to the use of VTT well in excess of Intel’s published maximum specification.
We’ve been trying for a while now to advocate a more intelligent approach to overclocking. Our loss should serve as an example for all as to the potential consequences of ignoring a little good advice. If nothing else, please don’t let our mistake become your mistake, too.
legolasyiu - Wednesday, April 16, 2008 - link
I learn my mistake with my AMD Athlon XP 2600+ overclocked. It didn't post with another motherboard, my dad had to go to AMD and get it replaced. It was Heat Sink with fan cooling.Well, there is always a physical limitation to everything - especially CPU with Motherboard. Is it a CPU VTT limit or motherboard's Cap?
Is it a physical limit? Did you use Water cooling?
sc3252 - Wednesday, April 16, 2008 - link
Quick, RMA it.Giacomo - Wednesday, April 16, 2008 - link
Does this warning apply to the previous 65 nm toys as well?Thanks for sharing, even if I'm not too convinced by your stats population.
Giacomo
brian_riendeau - Wednesday, April 16, 2008 - link
Is that CPU lapped too? Lapping could have damaged the CPU as well. With a sample size of 1, its really hard to blame the voltage specigically.