Athlon 64 for Quiet Power

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PERFORMANCE

The Athlon 64 is most assuredly a fast 32-bit CPU. Benchmarks can be found at every hardware site on the web, but just in case you’ve missed them, I’ll summarize: In all but a very few benchmarks the Athlon 64 stomps an equivalently priced Pentium 4. Not only that, but the Athlon 64 simply feels faster under normal use.

You’re probably asking, “What do you mean it feels faster?” Well, for comparison I have a Pentium 4 2.8 GHz machine at work, and an Athlon 64 3000+ machine at home. They both have 1GB of the same ram and 80gig 7200rpm 8mb cache hard drives. Under light use—web surfing, writing documents, writing code, etc—the Athlon 64 is just snappier. Windows, menus, animations, etc. respond quicker and feel faster on the Athlon 64 machine. I’m not alone in my feelings either. In a recent forum post our own Mike Chin writes:

“... my A64-3200 system [is] right next to my main P4-2.8C rig. Win XP Pro on both. No contest: The A64 runs faster & cooler. I don't mean benchmarks, I mean using the full range of apps I use daily -- Photoshop, Dreamweaver, Acrobat, Adobe InDesign, a bunch of web design tools... I've been gradually migrating to the A64 -- to turn it from backup machine to main machine.”

Most of this increase in speed and responsiveness is due to the integrated memory controller. Because of the Athlon 64’s memory controller, the delay from when an application first requests data to when it receives the first pieces of that data is much smaller than with a traditional northbridge-contained memory controller, thus increasing the perceived responsiveness of the application. To be fair, though, AMD is not the only one trying to increase the responsiveness of every day computer use. Intel’s HyperThreading helps to achieve just that.

HyperThreading is Intel’s name for their implementation of Simultaneous Multi-Threading (SMT). SMT is simply a way of allowing more portions of a CPU to be active at one time. To achieve this, an SMT-enabled CPU is actually exposed to the operating system as two CPUs. This way, the operating system can schedule two threads to run simultaneously. The CPU then sorts out which thread is actually running at any given time and in some cases can run portions of each thread in parallel.

Many people think that, because of HyperThreading, multi-tasking should be much smoother on a Pentium 4 than on an Athlon 64. While it is true that HyperThreading can provide a large benefit in multitasking situations, in my experiences the Pentium 4 is still significantly less responsive than the Athlon 64, even in situations involving heavy multitasking. I do software development work and most of the multi-tasking I do is during a compile. My Athlon 64 system is noticeably more responsive during a compile than my Pentium 4 system at work. Add to that the fact that the same code that takes 15 minutes to compile at work only takes 8 minutes to compile on my home machine, and you have a much more pleasant computing experience.

HEAT & POWER

Most people assume that all this computing power comes at a price — heat. Probably the biggest misconceptions about the Athlon 64 are in regards to its power consumption. The most often quoted number is AMD’s listed 89W Thermal Design Power (TDP). Many see that number and assume that the Athlon 64 dissipates as much heat as the Pentium 4, which Intel lists as having similar TDP numbers. The reality is that AMD and Intel arrive at their TDP numbers in very different ways.

In the next section I will refer to the following documents, anyone interested in the thermal details of these CPUs should download and read these documents in their entirety:

• AMD Athlon 64 Processor Power and Thermal Data Sheet (http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/30430.pdf)

• Intel® Pentium® 4 Processor with 512-KB L2 Cache on 0.13 Micron Process and Intel® Pentium® 4 Processor Extreme Edition Supporting Hyper-Threading Technology(1) Datasheet (http://www.intel.com/design/pentium4/datashts/29864312.pdf)

• Intel® Pentium® 4 Processor on 90 nm Process Datasheet (http://www.intel.com/design/Pentium4/datashts/30056102.pdf)

Here is a summary of TDP data from those documents:

TDP for for P4 and Athlon 64 processors
Model
Northwood P4
Prescott P4
Athlon 64
2.8 / 2800+
70
89
89
3.0 / 3000+
82
89
89
3.2 / 3200+
82
89 / 103
89
3.2EE
92
-
-
3.4 / 3400+ / 3500+
89
103
89
3.4EE
103
-
-
3700+ / 3800+
-
-
89
FX51
-
-
89
FX53
-
-
89

All figures rounded off.

As you can see Intel lists a different TDP for each CPU, while AMD lists the same TDP for all their CPUs. Obviously the Athlon 64 3800+ must draw significantly more power than the 2800+, so the only logical conclusion is that the 2800+ must draw significantly less than 89W. Even so it would still appear that, according to these charts, the Athlon 64’s power consumption is fairly close to the Pentium 4, right? To find the answer to that question we have to dig a bit deeper into the referenced documents.



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