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LOSTCIRCUITS
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| Intel's P4 820D and 670 More Power to Duallies | |
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(Review by MS September 3, 2005) |
| P4-670 |
Summary
Awhile ago, Intel released two processors, geared towards the high-end and the low-end of the market, respectively, namely the dual core P4 820D and the high frequency P4 670. Whereas it is possible to migrate from any other 600 or 500 series P4 on a 925 / 915 chipset based mother board to the 670, the 820D, as well as any of the other new dual core CPUs will require a new mainboard sporting either the 955X or else the lower end 945 chipset and, therefore, the "upgrade" will put a larger dent into the wallet than what the isolated CPU price would suggest. On the other hand, the 820 D is offered at a killer price, made possible through subsidizing by the chipset division that is clinging to every straw that could reel in some additional sales ... nay, we made up the subsidizing part..
In any case, we took the two superheroes and threw them into a deathmatch with the necessary bots in the form of AMD's offerings and Intel's own in-house competition. Of particular interest were the power numbers that we compiled in some cases to show the total CPU power consumption per workload. Read on to find out more ...
Thus far, symmetric multi processing, that is the use of more than one fully configured CPU as opposed to having for example one main processor and a math co-processor has been somewhat the oddball in the field of home computing. Two physically separate CPUs simply carried too much overhead with them to be a realistic and economic solution, not to mention the lack of support by the mainstream operating systems including Windows XP Home Edition. Multicore processors are only now emerging, even though they have been available for a few months, there are still limitations in the form of compatibility with the voltage regulator modules, with the BIOS or with the chipset per se. Add a logical division of the physical cores into emulated corelets in the form of HyperThreading and the compatibility and support issues are pushed one notch further but we are still not convinced of how much of this is marketing and product differentiation rather than technical issues.
In the green camp, AMD has spearheaded the multicore development as we see it happening right now, however, like them as you might, the cost of the cheapest dual core CPU alone exceeds that of an entry level HP or Dell computer. Suffice it to say that the latter are a far cry from being state of the art and are mostly assembled from somewhat obsolete warehouse inventory. On the other hand, there are these multicore CPUs, offering condensed power in a single package even at lower clock speed and somewhat reduced power. In the case of AMD CPUs, true multiprocessor solutions still enjoy the extra memory bandwidth through the dedicated near memory. In the case of Intel's Pentium4, it does not appear to matter too much whether there is a single dual core CPU or two single cores with SMP capabilities - the memory interfacing is about the same.
Dual Core technology a la Intel
What does matter though is that Intel is the first company to offer multicore CPUs to the broad masses, the 820 D is currently selling for about $200,- and change. On the other end of the spectrum is Intel's fastest core, the Pentium 4 670 running at 19 x 200 MHz on a quad-pumped host bus with a total of 6.4 GB total bandwidth. Needless to say that there is a substantial difference in price between the two processors, on the other hand, the question is, whether it is really worth going for an expensive CPU that is at the end of its own roadmap. Another factor needed to be taken into consideration is that just increasing the multiplier adds internal horsepower but also the system lag. In other words, what good is it to go to 3.8 GHz if the PSB is still running at 800 MHz, by extension, what good is running DDR2 at 667 MHz with 10.7 GB/sec bandwidth when the host bus constitutes a bottleneck at 6.4 GB/sec.
Then there is the way of playing it really Dumb: the "D" series has two cores, therefore, one can multiply the clock frequency by a factor of 2 and the result is a nominal 5.6 GHz CPU for about $200.- and change. Of course, this is not realistic unless....
... Unless one is talking about for example 3D processing, photorealistic rendering, possibly video editing and encoding. Even future games are supposed to potentially draw upon the extra horsepower of SMP, we had some very timid advances into that direction already with Quake3, albeit with some speed errors that negated the advantages of SMP in the final analysis. Finally, there is the question of power consumption. One thing that has been the topic of our discussions here at least for the last decade is the question whether any 3.8 GHz P4 (single core design) will draw more power or less than a dual core design running at a mere 2.8GHz. This question is even more interesting, since EIST, short for Enhanced Intel Speedstep architecture uses on-the-fly changes of the multiplier to a low of 14 x (which is the lowest value supported by the Prescott). This means that one possibility for power saving - by clockspeed reduction - does not even apply to the P4 820D, because it already is at the lowest value supported by the architecture.
This also gets us to the issue of the 800 MHz limitation of the PSB or host bus. If Intel were to increase the PSB to 1066 MHz data rate, this would automatically push the slowest Netburst processor to 3.73 MHz - and power saving via multiplier changing / clock speed reduction would not be possible. In other words, the only way to keep the CPU cool and the power consumption in check appears to stick with the 800 MHx bus speed. But then, the next question is how much of EIST is really happening; But I digress, what we are really interested in is what is the better CPU and as always, there is not a single answer but we do our best to provide the basics for anyone willing to make a more or less educated decision.
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Pentium4 820 D (dual core) |
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