AMD's 2.0Ghz Barrier

More than year ago everyone was talking about Barcelona's from AMD that would clock to 2.3 and even 2.66Ghz in 2007. However, these speeds have never been released. And, rather than asking why, not a single review site has mentioned it. The common pretense today seems to be that AMD never claimed that it would top 2.66Ghz in 2007 which, of course, it did.

It isn't hard at all to find evidence of AMD's intention to have K10's clocked as high as 2 or 2.6Ghz in 2007.

AMD promises 2.6Ghz Barcelona
Clearly, everyone (including AMD) expected Barcelona's faster than 2.66Ghz to be released in 2007 yet these were never released. The common excuse given by AMD proponents is that AMD didn't release faster chips as originally planned because, “It didn't have to.” However, there is good evidence that the reason had more to do with temperature and overheating than a warm and fuzzy feeling of being safely in the lead.

It is very rare to get proper numbers for thermal testing of AMD cpu's. Typically, overclocking is done with premium cooling and testing with the stock HSF never thermally stresses the CPU. For example, when Anandtech originally reviewed X6800, they used a massive Tuniq Tower. This is, of course, nothing at all like what is shipped in the vast majority of computer systems. A term that often gets tossed around is "on air". However the truth is that high end air coolers today are as good as liquid coolers used to be four or five years ago. Thus the term "on air" now means very little. Cooling your CPU "on air" with something the size of a transmission cooler is not much an accomplishment. But, if you could overclock "on air" with the stock HSF, that would be an accomplishment indeed. Unfortunately, review sites seem to want to do thermal testing with a stock HSF about as much as they would like to feed a tank full of hungry piranhas by hand.

It appears that we only got some halfway informative numbers from Anandtech by accident when they were reviewing a cooler instead of the processor itself. I've talked about this information in an earlier article but I'm going to revisit it along with other information since people still seem confused about Barcelona's thermal limitations.

In Anandtech's Case cooling in the second chart: CPU Temperature Under Load, we have some data. Notice that at the stock clock speed of 2.93Ghz with the stock HSF, X6800 is reading 56 C. Now, the article says, "The stress test simulates running a demanding contemporary game. The Far Cry River demo is looped for 30 minutes and the CPU temperature is captured at 4 second intervals". Unfortunately, Anandtech's assumption is a bit off since Far Cry does not really thermally stress the core. According to the Barcelona Temperature Guide:

AMD provides a test program, Thermal Analysis Tool (TAT), to simulate 100% Load. Some users may not be aware that Prime95, Orthos, Everest and assorted others, may simulate loads which are intermittent, or less than TAT. These are ideal for stress testing CPU, memory and system stability over time, but aren't designed for testing the limits of CPU cooling efficiency.

Orthos Priority 9 Small FFT’s simulates 88% of TAT ~ 5c lower.

So, if FFT is 5C lower then Far Cry would be less than that. The Guide also clearly states Tcase Load should not exceed ~ 60c with TAT, and 55c with Orthos.

But, at 56 C we have already exceeded 55 C. And, that would be if we were running FFT. Since we are only running Far Cry the real temperature is probably closer to 60 C at full load. Now, someone will probably claim that that is okay because you would never hit full thermal load under normal circumstances. Unfortunately, that is already figured in. As stated in the guide: 50c is safe. 50c Tcase is a safe and sustainable temperature. 55 or 60 C are not safe or sustainable temperatures. Even though the maximum spec is 60 C, 60c is hot.

I have seen others claim that 60 C was fine because it didn't exceed the maximum rating. However, this is not the way the rating works. 60 C is the maximum for TAT only because no other program will ever reach this stress level. So, it is clear that X6800 with stock HSF will indeed exceed the factory cooling specs at stock speed. This is why AMD has not released a 2Ghz quad core.

But . . . what about dual core? Even if the quad core processor is running too hot with stock HSF maybe the dual core isn't. As I've already mentioned, these types of tests seem to be avoided like the plague by regular review sites. So, we need something obscure. However, as luck would have it, we do have something out of the ordinary at Digit Life where X6800 (2.93 Ghz) dual core is reviewed. These conditions are very unusual because he tests in his un-air conditioned apartment. In Moscow apartments, unconditioned for several days, the standard daytime temperature was within +25—+30°C. In this case the environment temperature was +28°C. 28 C is 82 F. This would not be unusual for Indiana in the Summer either. But, he uses the stock HSF. And, let's see what happens:

it didn't even occur to us that new AMD Barcelona processors could spring such a surprise with throttling...) Yes! It was throttling!

The chart is excellent because it compares the stock HSF to a better cooling solution. We can see that none of the common benchmarks really thermally stress the cpu. The one that stressed it the most was the Solidworks CAD & CAE benchmark. The chart only shows an 11% drop because it is a total score. However, The results of the overheated processor are very low in two applications out of three: SolidWorks 2005 and Pro/ENGINEER Wildfire 2.0. This is proof positive that even with a regular application that dual core C2D is busting the thermal limits when running at 82 F ambient. The author says that there was no thermal throttling at 72 F ambient.

Now, let's look at that chart again. Notice that with the 3D Shooter Games (F.E.A.R, Half Life 2, Quake 4, Unreal Tournament 2004) the drop is only 3% versus the 11% we saw with CAD. This again casts doubt that Anandtech was doing anything thermally stressful with Far Cry.

So, AMD did not release a 2Ghz processor in 2007 because they couldn't. Such a processor would have exceeded the factory's own limits when running routine applications at ambient temperatures common in the Summer. However, we also know that AMD has steadily improved the thermal properties of its C2D chips with each revision. It is possible that one of the newer revisions of C2D would be capable of going over 2.66Ghz without busting the factory's thermal limits. After all, one would assume that simply lowering the TDP would help and we know that TDP has come down. However, I'm not entirely sure that 65nm is actually an improvement. For example, if a given 65nm chip has the same TDP as a given 90nm chip then logically the 65nm chip would concentrate the heat into about half the die area. This would seem to be more likely to create hot spots rather than less.

I'm quite certain that AMD will indeed get chips out that exceed 2.66Ghz. And, I'm pretty certain that if AMD doesn't do it in Q4 of this year that Q1 08 should be reasonable. It might happen with 65nm as many expect but I can't see any reason why it couldn't happen with 90nm in another revision or two if 65nm wasn't up to at first. In other words, AMD would move to 65nm anyway to reduce die size even if it didn't make any major strides in power draw at first. However, the talk has been that 65nm at AMD is much better with power draw than 90nm. I guess we need to take that with a grain of salt since it was claimed in January 2007 that AMD had K10 samples hitting 2.0Ghz. It would be nice to have some up to date comparison information with newer C2D's to see if the thermal limits have been improving over time (which they likely have). But, since the information we do have about stock cooling is nearly accidental that seems very unlikely. We may just have to wait until Q4 and see if any 2 or 2.0Ghz 65nm chips appear.