Dual-Core Servers: AMD or Intel?

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Ever since AMD's entry to the server market with its Opteron processor, system builders have faced the question of which chips to use in their servers: AMD or Intel?

Is there really any difference? The short answer is yes. But what does a system builder really need to know before fielding systems based on these rival architectures? In this Recipe, we will go beyond the marketing hype to get to the heart of the matter " creating server specs for your customers that will achieve best performance for their application at the lowest overall cost.

For a price-comparing illustration, I will use a Bill of Materials (BOM) that includes motherboard, processor and memory for both the Intel and AMD server platforms. To keep the comparison as objective as possible, all other subsystems of the server " such as I/O and storage " will be assumed identical, and therefore irrelevant to our discussion. Motherboards by Tyan and memory by Kingston are used for example here; comparable parts from other manufacturers can be substituted at similar price points. My pricing data is from Tech Data Corp. and is current as of June 15, 2007.

The first useful piece of information to glean from this table is that the initial build for an Intel Xeon-based server will be about 25 percent more expensive than its AMD Opteron counterpart. Also, this price gap will widen as more memory modules and processors are added. That is where the majority of the difference lies.

So, assuming for a minute that we decide to go with the Intel Xeon-based system, what are we getting for that 25 percent additional cost? Does the Intel processor perform 25 percent better than the AMD Opteron? That depends on your application. Let's take a look at the differences between the processor architectures, memory controllers and motherboard chipsets to get the low-down on this subject.

At first glance, the larger L2 cache available to the Intel Xeon might lead one to believe that it would be a better performer, hands down.

But it's not that simple. AMD's Direct Connect Architecture eliminates the bottleneck associated with the Front-Side Bus (FSB) architecture that Intel uses, giving the AMD chip a 50 percent greater bandwidth to off-chip resources. This accounts for the majority of data transactions.

Also, the Opteron gains additional efficiency by integrating its memory controller directly onto the chip itself, rather than routing memory traffic through a bus, as the Intel Xeon does. Under maximum load, the Opteron will use slightly more power -- about 5 percent more wattage. But under partial loads, the Opteron is more energy-efficient than the Intel Xeon.

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