Desktop CPU Power Survey, April 2006

CPUs|Motherboards | Power
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TESTED PROCESSORS

The table below lists all the processors we tested, ordered and roughly matched by price. All the prices those officially cited for large corporate customers, in US$, as listed here: AMD Processor Pricing and Intel Processor Pricing. This may not be the best way to compare, as prices change so quickly, but given the huge range of processing performance represented here, it is probably about as good as any. There is a rough performance match. The A64-3000+ and P4-630 are relatively close, as are the A64 X2 3800+ and Pentium D 930. The A64 X2 4800+ and Pentium D 950 might also be a reasonable performance contest as well. The Core Duo T2600 probably won't stand up to the desktop top dogs in performance, but the price matches. In any case, the table is simply a way to list all 15 processors tested in one simple table. (There are only 14 listed; the missing one is a second A64-3500+ with a different core stepping.)

AMD
PRICE
INTEL
Sempron 3400+
754, 2GHz / 256KB, 64-bit, Venice
$120
Athlon 64 3000+
939, 1.8GHz / 512KB, 64-bit, Venice
$140
$178
Pentium 4 630
775, 3.0GHz / 2MB, 64-bit, Prescott
Athlon 64 3500+
939, 2.2GHz / 512KB, 64-bit, Venice & Winchester
$205
$210
Pentium D 820
775, 2.8GHz / 2MB, 64-bit, Smithfield
Turion 64 MT40
754, 2.2GHz / 1MB, 64-bit, Lancaster
$268
Athlon 64 X2 3800+ Processor
939, 2.0GHz / 2x512KB, 64-bit, Toledo
$301
$316
Pentium D 930
775, 3.0GHz / 2x2MB, 64-bit, Presler 65nm
Athlon 64 4000+ Processor
939, 2.4GHz / 1MB, 64-bit, San Diego
$341
   
$424
Pentium M 770
479, 2.13GHz / 2MB, Dothan
   
$605
Pentium 4 670
775, 3.8GHz / 2MB, 64-bit, Prescott
Athlon 64 X2 4800+ Processor
939, 2GHz / 2x1MB, 64-bit, Toledo
$643
$637
Core Duo T2600
479, 2.16GHz / 2MB, Yonah
$637
Pentium D 950
775, 3.4GHz / 2x2MB, 64-bit, Presler 65nm

An obvious but important fact to point out is that an articles like this is a snapshot of moving targets. It's a survey that's relevant today. Within six months, especially in this year of major processor line changes by both Intel and AMD, the whole processor scene may be changed, and we will probably be scrambling to put together another survey relevant for that time.

CPU SAMPLE VARIANCE

The power consumption characteristics of processors varies from sample to sample within the same model and stepping. It can vary as much as >10%, according to some sources, although it is probably considerably less than that on average. It is exactly the same variance that makes some individual processor samples easily overclocked (or undervolted) and others not overclockable at all. We have a mix of samples, mostly provided directly by Intel and AMD, mostly only one sample of each model. Our results are probably more or less repeatable but it would be a surprise if anyone obtained identical results with a similar collection of samples. Our results are good general indicators, but please don't assume that because our sample managed to run stable at 1.15V on our particular motherboard that all samples of the same CPU model can do the same. Also, don't base your buying decision between two closely ranked processors on the basis of any single result we report. Price, suitability, availability, peripherals, ease of implementation — these are all important buying considerations.

In recognition of these sample variances, which have always existed, AMD began embedding sample-specific information about Thermal Design Power (TDP) and TCaseMax (maximum casing temperature) in E-Revision A64 processors some time last year. These are the chips that contain this information include:

* Athlon 64 (Venice, San Diego)
* Athlon 64 FX (San Diego)
* Athlon 64 X2 (Manchester, Toledo)
* All Rev E Opterons and Dual Core Opterons

TDP and TCaseMax are closely related to each other, moving higher and lower together. A processor cannot have low TDP and high TCaseMax or vice versa. For each model, there is a broad enough range of TDP/TCaseMax so that some people are very interested in cherry picking. Unfortunately, this information is not visible on any marking on the outside of the processor or the packaging. The processor has to be plugged into a motherboard and run before the information can be accessed. There is a little utility written just for this purpose: AMD64 TCaseMax v1.18. Here are some screenshots from this program.

The processor on the left is a Winchester core (D0 revision) and lacks the sample-specific TDP info. The Venice core (E3 revision) on the right has it: 67W TDP, which is the stock spec for this processor. It suggests this sample is run-of-the-mill for overclocking or undervolting.

The A64 X2 3800+ on the left is a more recent E6 revision (also called stepping) with a TDP of 65.6W, which is considerably lower than the standard 89W spec for this part. The same is true of the X2 4800+ on the right; 85W is much lower than the standard 110W TDP spec for this model.

The 44.1W TDP 3000+ E3 stepping on the left has the lowest TDP of any A64 in this roundup. The standard spec is 67W. The 4000+ E4 on the right is also a cool operator, coming in 39W below its standard 89W spec. Both of these samples should be good undervolters.

AMD says that the average TDP of most of their processor models has been dropping steadily over time. This is the result of a conscious effort, of continuous refinement in the manufacturing process. It means that while you might still find 89W 4000+ samples, the number of such parts coming off the line is much lower today than when the part was first introduced. The 50W samples, on the other hand, may not even have existed when the model was first introduced.

Intel does not embed individualized TDP information with its current line of Prescott, Smithfield, and Presler core processors. Variances certainly exist among Intel processors, but we have never had many of the same model to get any sense of how much they vary in thermally. The Prescott P4 is infamously hot, and while there have been improvements to help manage the heat better since their initial release, increasing clock speeds and memory cache sizes have not helped much. Enhanced Intel Speedstep (EIST) dynamic clock/voltage adjustments similar to AMD's Cool'n'Quiet, has helped, along with C1E halt state support. Both help reduce idle power but do nothing for power draw at load. While idle power consumption is more important for overall energy efficiency of the PC, it's the maximum CPU power peaks that the cooling system must be capable of handling. The tendency toward very high maximum power demand of the Intel desktop processor line has not changed, with the exception of the mobile offshoot Core Duo / Solo processors. We will have to wait for Conroe later in the year for an Intel desktop processor with TDPs boasted by AMD processors today.



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