Overclocking Intel's New 45nm QX9650: The Rules Have Changed
by Kris Boughton on December 19, 2007 2:00 AM EST- Posted in
- CPUs
An Unexpected Loss of Performance at Higher Speeds
It looks as though Core 1 is having trouble keeping up with the other three
We first suspected our motherboard's VRM circuitry might have been overheating while supplying the high load current. If this were the case the PWM IC would communicate with the processor using the PROCHOT pad and the CPU would respond by modulating an internal clocking signal to each core thereby artificially lowering the load and allowing the VRM to cool - a failsafe meant to save the VRM should things start to get too hot. Eventually our frustration in the matter led us to modify our board by disconnecting the control signal altogether. Unfortunately, there was no change.
We discussed the possibility of having discovered an undocumented erratum, thinking that maybe some internal control logic was at fault. The Analog Devices ADP3228 PWM controller used on the ASUS P5E3 motherboard, designed in compliance with Intel's new VRM 11.1 specification, includes a new power management feature intended to improve power circuit efficiency during periods of light loading. When directed by the CPU the VRM essentially disables four of the eight power delivery phases until they are later command back on. (This is not unlike the concept put to use in the automobile industry wherein half an internal combustion engine shuts down while cruising in order to improve fuel economy.) However, we are unable to completely rule out a possible incompatibility as no one is aware of how to go about disabling this feature.
In fact, we believe what we are seeing may be nothing more than a CPU protection mechanism in action. The Core 2 family of processors is extremely resilient to abuse - reports of failures due to overvoltage or over current incidents are exceedingly rare. Features such as these work by clamping processor input voltage (and current) to tolerable levels in order to prevent permanent damage. Further testing reveals we have some level of control with regards to the "throttling" - it seems that by slightly lowering the VID, and thus in turn the CPU supply voltage, we are able to complete testing at some of the same frequencies with no noticeable performance degradation issues. Could it be possible that we found a processor protection limit with nothing more than common water-cooling? Normally, such discoveries are the domain of those that freeze their CPUs with one or more rotary compressors or copious amounts of liquid nitrogen. Given the enormous power increases observed at these higher speeds due to what might be a processor capacitance effect, we cannot help but wonder if these new limitations are an unintended consequence of Intel's 45nm process.
If what we believe is true the implications could be enormous. The need for certain industries built on delivering high-performance cooling solutions to the overclocking community would be largely invalidated. What's the point in spending more money on a more effective heatsink if there's nothing to gain? With that said, we honestly believe a new direction in CPU overclocking may soon be upon us. While there will always be those that continue to push processors to their absolute limits, the majority of us will find our new "performance" benchmark in efficiency. This makes sense though - the market has been heading this way for years now and overclockers may have simply chosen to ignore the obvious. The multi-core era we now live in places a heavy emphasis on performance-per-watt figures and other measurable efficiencies. Does anyone else find it odd that Intel's flagship product, the QX9650, comes at exactly the same speed bin as the previous 65nm offering? All this talk of improved performance and efficiency and not even a measly frequency bump - perhaps Intel is trying to tell us something.
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Aivas47a - Wednesday, December 19, 2007 - link
Great article. You guys have really been distinguishing yourselves with in-depth work on overclocking the last few months: exploring obscure bios settings, tinkering with "extreme" cooling -- keep it up!My experience with a qx9650 so far is very similar to yours: easy scaling to 4 ghz, difficult scaling after that with 4.2 ghz being the practical max for regular operation (folding, etc.).
One issue I will be interested to see you address in the future is fsb overclocking on yorkfield. So far I am seeing yorkfield top out at lower fsb (450-460) than was possible for kentsfield on a comparable P35 or X38 platform. That is not so significant for the unlocked Extreme Edition chips, but could make it difficult to achieve the magic 4 ghz with the q9550 and especially the q9450.
Aivas47a - Wednesday, December 19, 2007 - link
Great article. You guys have really been distinguishing yourselves with in-depth work on overclocking the last few months: exploring obscure bios settings, tinkering with "extreme" cooling -- keep it up!My experience with a qx9650 so far is very similar to yours: easy scaling to 4 ghz, difficult scaling after that with 4.2 ghz being the practical max for regular operation (folding, etc.).
One issue I will be interested to see you address in the future is fsb overclocking on yorkfield. So far I am seeing yorkfield top out at lower fsb (450-460) than was possible for kentsfield on a comparable P35 or X38 platform. That is not so significant for the unlocked Extreme Edition chips, but could make it difficult to achieve the magic 4 ghz with the q9550 and especially the q9450.
Doormat - Wednesday, December 19, 2007 - link
Though its somewhat disappointing on the rumors that Intel has postponed the launch of their QuadCore desktop chips from January to March.Sunrise089 - Wednesday, December 19, 2007 - link
I agree with everyone else - really top notch stuff here.1 glaring typo though, from the first page: "Moving to a smaller node process technology allows for the potential of one or two things to happen. " - the "or" should be an "of"
ChronoReverse - Wednesday, December 19, 2007 - link
It seems that ATI cards have less of a drop going from XP to Vista (down to zero and even negative sometimes). It might be instructive to use that for the charts that compare Vista to XP for 3D (e.g., the 3Dmark06 benchmark).melgross - Wednesday, December 19, 2007 - link
Capacitors have their capacitance turned into reactance at higher frequencies. Anything that qualifies, in a circuit, as a capacitor, such as two wires riding in parallel, will have, to a greater or lesser extent, the same problem in the design.Reactance rolls off high frequencies. More power is required to offset that.
This is the same problem whether dealing with low frequencies in an audio circuit (where it may be less of a problem), or a high performing computer. It's almost impossible to eliminate all stray capacitance from a circuit, and more circuitry becomes capacitive at higher frequencies. This will only increase as a problem as we get to smaller processes, such as 32nm.
andyleung - Wednesday, December 19, 2007 - link
I am very interested in the performance of these new CPUs. They are Quad-Core and they are good enough to perform some heavy duty business tasks. Wondering how they work with JEE performance.BLHealthy4life - Wednesday, December 19, 2007 - link
This article is a perfect example of what makes Anandtech so great. Anandtech has the most brilliant and most technically savvy guys on the internet.Very rarely will you fine any other website review pieces of hardware with such intricate detail for hardware specs and the technology behind it.
Great work guys!
BL
kkak52 - Wednesday, December 19, 2007 - link
really an informative article.... good work!Bozo Galora - Wednesday, December 19, 2007 - link
A 10+ article, especially the vdroop section.Its nice to see something on AT like the old days thats cuts through the BS and actually gives real usable info.
Quite a tour de force.
Nice work.