Desktop CPU Power Survey, April 2006

CPUs|Motherboards | Power
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March 6, 2006 by Mike Chin

This article began as a relatively simple follow-up to Turion 64 on the Desktop, posted in mid-February. It was meant to answer the question most often asked by readers of the Turion 64 article,

"So how does the Turion 64 fare against the latest Athlon 64s, in terms of power efficiency, performance, ease of use on the desktop and price?"

It's a pertinent question for many reasons:

  1. The same basic core is at the heart of the Turion 64 and the Athlon 64.
  2. The power efficiency of the Athlon 64 has been improved by AMD, quietly but steadily. The "E" steppings and beyond are particularly cool-running, and may actually approach Turion 64 levels.
  3. If an Athlon 64-939 is almost as cool as a Turion 64, it is a better choice to run on a desktop system for most people, due to ease of implementation, lower cost for similar clock/cache, and the superior performance of socket 939 motherboards — due mostly to dual channel memory support but also because the most ambitious motherboards are socket 939.

Somehow, during the research to compose a reasonably complete answer to the above question, the piece ballooned into something more ambitious. We ended up examining almost every recent CPU in the SPCR lab on several different platforms to answer not only the question above, but also the question,

"What is the best power efficiency achievable with currently available AMD and Intel processors that can be used on a desktop PC?"

It is not possible to answer this question comprehensively with precision without access to dozens of processors and test beds, and an enormous amount of time, manpower and resources. Still, we managed to get a good sampling of the processor families that represent the vast majority of CPUs actually being bought and used for desktop PCs today. We used the test methods that worked well for the Turion 64 article.


Some of the gear assembled for this article.

WHY ASK THE QUESTION?

In the above question, the phrase "best power efficiency" means lowest power consumption, which relates directly to the amount of power demanded and generated into heat by the CPU, and to a lesser degree, the motherboard. (More on the latter later.) The relevance of this question is obvious for those who seek to minimize PC noise: The cooler the PC, the less airflow required to cool it, which means fewer and/or slow spinning fans that make less noise.

We won't go into PC silencing in any detail here. Suffice it to say that reducing heat means cutting down on power consumption. A number of methods for doing so have become popular at SPCR, including:

  • Undervolting and underclocking: Lower voltage chips running at slower clock speed consume less power.
  • Deliberately choosing low-end parts, as they are often slower and lower voltage than the latest and greatest.
  • Choosing more efficient parts, with high performance-per-watt ratios.
  • Using parts designed for the laptops (such as HDDs and CPUs), which consume minimal power to conserve battery life.

The power and heat issue is relevant to everyone else in a variety of ways:

  • Environmental: High power efficiency means lower energy consumption becomes a significant environmental issue. Computers do represent a significant percentage of electricity consumption not only directly but indirectly with increased air-conditioning cost in enterprise applications due to their added heat.
  • Performance: High power efficiency means that the electrical and thermal stress in high performance computers can be reduced, and make even higher performance achievable. When the high expense and complexity of delivering high power into a PC and then evacuation the ensuing heat is considered, a cooler, more efficient CPU makes perfectly good sense for dedicated gamers and others who need or seek extreme performance. Achieving extreme clock speeds requires the best cooling; less heat is a good starting point.
  • Financial: Both of the above points touch upon the significant expense, both short and long term, directly associated with low power efficiency. High power efficiency means lower costs all around. The costs of other components drop when the CPU consumes less power, from the power supply to the heatsink/fan to the enclosure cooling requirements. Other cost factors external to the PC — including Uninterruptible Power Supplies, air-conditioning, and direct electricity costs — all drop when less power and heat are in the PC. The savings become very serious when large numbers of computers are considered, as in big enterprises like government agencies and corporations.

As we noted in the Turion 64 article, hardware manufacturers have recognized the importance of reducing power. High efficiency power supplies are increasingly more common, and Intel and AMD both identify performance-per-watt as a key benchmark.



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