First Look at Core i7-975 XE: D0 Processor Stepping in Action

Our lab managed to get an engineering sample of a not yet announced Core i7-975 XE processor that is based on the new D0 processor stepping. Today we are going to check out the features of this new processor core and figure out its advantages over the previous Nehalem C0 processor stepping.

by Ilya Gavrichenkov
04/21/2009 | 07:17 PM

Detailed Review: Nehalem Speeding Up: Intel Core i7-975 XE and Core i7-950 Review


It is no secret to anyone anymore that in the nearest future we should witness numerous new CPU launches. Both, AMD and Intel, are going to refresh their model lineups significantly and to raise the performance bar of their most expensive processors. AMD is preparing to launch their Phenom II X4 955 Black Edition, while Intel is working on another Core i7 – the i7-975 Extreme Edition model. In fact, the launches of such expensive processors rarely excite the general public too much. Solutions like that enhance the manufacturer prestige and serve mostly as a sort of theoretical demonstration of the technological advancement. In reality, these new processors do not differ that much from their predecessors: only their clock frequency is higher. From the consumer standpoint it is much more significant that the launch of new top solutions inevitably causes prices on the other CPU models to go down.

However, launches like that sometimes give us some other pleasant surprises. One of these surprises will shortly be delivered by Intel: the launch of Core i7-975 XE will take place together with the introduction of the new enhanced Nehalem processor stepping called D0. And luckily, Core i7-975 XE processors will be far not the only one to feature this new core. Intel will little by little introduce it into other Core i7 models. Moreover, the first solutions based on the new D0 processor stepping should start selling as Core i7-920 in the near future.

Therefore, we decided not to wait for the Core i7-975 XE official launch date in order to tell our readers about the changes made to the Nehalem D0 processor stepping. It is a very acute question for many computer enthusiasts, if these enhancements are worth waiting for and if they should search specifically for the CPUs with the new processor stepping. By a lucky chance we managed to find a preproduction engineering sample of the new Core i7-975 XE processor, which will help us today to investigate the peculiarities of the new D0 processor stepping.

D0 Processor Stepping: a Little Bit of Theory

Intel usually warns their closest partners about any changes in their products architecture or functionality. The same happened with the new processor stepping: they sent out the corresponding informational bulletin back in January 2009. Although, it was not too informative and told pretty much the following about the new stepping:

«The electrical, mechanical and thermal specifications remain within the current specifications. Intel anticipates no changes to customer platforms designed to previous Intel guidelines».

In other words, Intel engineers didn’t promise any evolutionary changes in the features of their processors based on the new core. However, Intel’s official claims about the identity of different processor steppings is barely a good argument for computer enthusiasts. According to our practical experience, even minor enhancements of the processor core may sometimes result into a noticeable practical improvement of heat dissipation, power consumption and overclockability. That is why experienced users always try to get their hands on processors featuring the latest core revisions. Especially, since in our particular case it is not that hard to distinguish between the CPUs on D0 processor stepping from their predecessors. Besides the core, Intel will also change one of the marking elements.

Also, Core i7 processors with new D0 processor stepping receive a new CPUID classifier that will now be equal 0x000106A5 (instead 0x000106A4 for the previous generation CPUs with C0 processor stepping). Therefore, to ensure correct operation of the new processors, mainboard manufacturers will have to update their BIOS code and include the support for the new core version into it. Luckily, the leading mainboard manufacturers have already done it, so you shouldn’t worry about compatibility issues.

Due to new CPUID, diagnostic utilities recognize the new processor core correctly. For example, here is the screenshot from the CPU-Z utility for our Core i7-975 XE:

Note that so far D0 processor stepping exists only in two types of Core i7 processors: the latest mass production Core i7-920 (new CPUs have SLBEJ S-Spec) and in Core i7-975 Extreme Edition engineering samples that are not retailing yet.

Testbed and Methods

Since we got our hands on the engineering sample of the new processor stepping, we performed a brief express-test in the following platform:

We took the previous Extreme Edition solution – Core i7-965 XE (C0 processor stepping) – to compare against our today’s hero – Core i7-975 XE. We have already reviewed the 965 XE model before, so please see our article called New Hit from Remake King: Intel Core i7 Review for details.

Power Consumption and Heat Dissipation

It is evident that it doesn’t make sense from the performance prospective to compare the CPUs with new and old processor stepping. Since Intel didn’t introduce any new technologies and didn’t make any architectural changes, CPUs with C0 and D0 processor steppings working at the same clock speeds will perform equally fast in regular benchmarks. That is why it is not very interesting to dwell on performance of the new Core i7-975 XE in our today’s article. However, the heat dissipation and power consumption measurements are, on the contrary, extremely interesting to perform. This is what we are going to do next.

First of all, we measured the temperature and full power consumption of the entire testbed (without the monitor) with both CPUs in idle mode, without any load. The tests were run with the CPU clock speed at 2.66GHz and 3.33GHz. We picked these particular settings because the first one is the nominal speed of the Core i7-920, while the second one – is the nominal frequency of the not announced yet Core i7-975 Extreme Edition CPU. During our tests C1E and Enhanced Intel SpeedStep power-saving technologies were enabled.

The obtained results indicate one thing: power-saving algorithms implemented in Nehalem CPUs with different processor steppings work almost identically. Both of them drop their frequency in idle mode to 1.6GHz, so we see almost the same temperature and power consumption. However, I have to say that Enhanced Intel SpeedStep technology works more aggressively by the CPU on D0 stepping. We saw the processor Vcore drop down to 0.912V under zero workload, while the CPU based on the old core dropped its core voltage only to 1.152V. Nevertheless, it barely affects the practical power consumption and heat dissipation readings.

The second part of our experiments dealt with thermal and electrical characteristics during maximum CPU utilization. We used 64-bit Linpack suite with LinX 0.5.8 shell. According to our tests, this combination warms up Nehalem processors best of all.

Processors power consumption and heat dissipation during stress-tests are no longer as unanimous as we have just seen in idle mode. New D0 processor stepping demonstrates evident advantage over the preceding core. The enhancements made to it provide a tangible improvement of the power consumption compared with the CPU on the old core version of up to 10-15W. Of course, the operational temperature of the CPU on D0 processor stepping also lowers.

So, despite all Intel’s claims, the CPUs on new processor stepping do have pretty definite advantages over the predecessors. They are more economical, which is a very good feature of the enhanced new core. Moreover, it should inevitably affect their overclocking potential, which we are going to check out next.


First of all we decided to see how well the new CPU with D0 core stepping can overclock without any voltage increase past the default value. The Core i7 CPUs with C0 processor stepping that have been in the market so far, have worked stably at up to 3.6GHz frequency in the same conditions. Further overclocking required higher Vcore.

D0 processor stepping proved suitable for work at higher frequencies. Our test Core i7-975 XE processor remained absolutely stable at 3.73GHz with Vcore set at 1.2V, which was the nominal setting for our particular sample.

As you can see from the screenshot, we used the opportunity to increase the clock frequency multiplier over its nominal value, which is available by Extreme Edition processors. However, it doesn’t diminish the importance of the obtained result: it is evident that processors with D0 stepping will be extremely demanded among computer enthusiasts who not only want to achieve maximum performance, but also care about power consumption and heat dissipation levels of their systems.

However, it is too early to wind up our discussion just yet. Let’s see what results we could achieve during Core i7-975 XE overclocking with the help of existing voltage adjustment options. The lower heat dissipation of CPUs with D0 processor stepping should be very helpful for overclocking success. As you should remember, it was increasing heat dissipation that limited the overclocking of the previous-generation Core i7 processors. It called for very advanced cooling solutions to fight that heat. Therefore, 4GHz frequency achieved with air cooling alone has been considered a very good result for the Core i7 CPUs. Our tests showed that the new Nehalem processor stepping allows you to easily pass this threshold.

As we continue working with an unlocked clock frequency multiplier, we could get our system to work stably at 4.13GHz. Vcore was increased to 1.36V. Note that with these settings during the stress-test the processor core temperature didn’t exceed 92°C, which suggests that we can hope for even better overclocking results. Unfortunately, further increase in the clock frequency multiplier caused system instability.

When we overclocked our CPU by changing the BCLK base clock generator frequency, the results again didn't improve significantly. With the multiplier at 21x (supported by any Core i7 CPUs) our processor reached 4.16GHz frequency:

The screenshot shows that the Vcore was set at 1.39V and the resulting frequency of 4.16GHz was obtained as 21 x 198MHz. We selected these particular settings trying to show what the Core i7 processors base don new stepping are capable of without the unlocked clock frequency multiplier. Also note that by raising the BCLK frequency to 198MHz we had to increase the Uncore CPU voltage to 1.255V. During the stress-test of an overclocked processor we saw that the temperatures were approaching critical heights. Maximum temperature during our test session reached 96°C. So, overclocking can only be improved with more advanced cooling solutions.

Although the frequency gain during overclocking was pretty significant, it is still too early to claim that the new D0 processor stepping will be a breakthrough overclocker solution. Yes, CPUs based on the new core version overclock better than their predecessors. And most importantly, they dissipate less heat during overclocking than the CPUs on C0 processor stepping. However, we do not see any overwhelming advantage. Of course, we can’t make any general conclusions after testing only one single CPU sample. However, the preliminary results reveal no significant difference between overclocker potential of Core i7 CPUs based on new and old processor stepping: only around 200MHz.


Although Intel doesn’t consider the launch of the Core i7 CPUs on the new D0 processor stepping to be any kind of a milestone, we think differently. Our short express-test session showed that CPUs using different processor steppings differ by their consumer qualities. And even though there may be no real difference in performance tests, all other features may differ quite dramatically.

Among the improvements we discovered in the new D0 processor stepping are lower practical heat dissipation and power consumption and a slight improvement of the overclocking potential. I believe it is quite enough to say that Intel engineers have made another small step towards making their flagship solution even better. Partially due to this small step forward we will soon welcome a new member of the Extreme Edition family – Core i7-975 XE with higher 3.33GHz nominal clock speed and the same thermal and electrical characteristics as those of the predecessor – Core i7-965 XE.

So, if you are looking to get yourself a high-end LGA1366 system, we strongly recommend waiting for Core i7-975 Extreme Edition, especially since it is launching in about a month already. However, you can get your hands on a CPU with a new core even sooner than that: Core i7-920 with a D0 processor stepping should start selling any day now. And according to the first lucky owners, these CPUs can absolutely unveil all the advantages of the new core, just like the upcoming Core i7-975 XE.