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Sizing up the Xeons and Opterons in our test
Intel, of course, hasn't been sitting still since we last looked at its server/workstation-class processors. The firm is now shipping a new E stepping of its 45nm Xeons that reduces power draw and allows for slightly higher clock frequencies. All of the Xeons we tested for this review are based on E-stepping silicon. We had intended to review these Xeons in a separate article but weren't able to complete it before this one, so we have a range of new-to-us products to test, based on multiple different Intel server- and workstation-class platforms.

The most direct competition for the Shanghai Opterons we've tested is the Xeon E5450, a 3GHz quad-core part with a 1333MHz front-side bus. We've tested the E5450 on Intel's highest-volume server platform, known as Bensley. This platform, based on the Intel 5000P chipset, is getting a little long in the tooth and lacks a few features, like support for a 1600MHz FSB, 800MHz FB-DIMMs, and a full-coverage snoop filter. However, it is still the predominant Xeon server platform, and is thus the best basis of comparison versus the Opteron systems we're testing. The Xeon E5450 is priced at $915 in volume, quite close to the $989 price tag of the Shanghai Opteron 2384. The two chips also share similar thermal envelopes; the Xeon E5450 is rated at an 80W TDP and the Opteron 2384 has a 75W ACP. (Assuming you buy AMD's arguments about its ACP ratings, at least, the two should be similar. We will test power consumption ourselves, regardless.)

We have also, of course, included AMD's best 65nm Opteron within this same thermal envelope, the 2356, to see how it compares to Shanghai.

Intel's 45nm Xeons extend into higher-performance and lower-power territory in some interesting ways, as well. The low-voltage Xeon L5430, for instance, has specs very similar to the E5450—quad cores, 2.66GHz core clock, 1333MHz bus, 12MB total L2 cache—but comes with a TDP rating of just 50W. For our testing, we've mated it with a very intriguing low-power server platform from Intel, known as San Clemente.

This is our first look at San Clemente, which Intel hasn't pushed especially hard in the mainstream server or workstation spaces. Instead, Intel has aimed it primarily at dense blade servers and embedded systems like routers, SANs, and NAS boxes. That's kind of a shame, since the Intel 5100 MCH at the heart of San Clemente makes a key power-saving move, shunning Fully Buffered DIMMs for registered DDR2 memory modules just like Opterons use. FB-DIMMs allow for higher total system memory capacities, but they exact notable penalties in terms of both memory access latencies and power consumption. San Clemente's power consumption could be quite a bit lower than Bensley's, as could its memory access latencies. Like Bensley, San Clemente has dual, independent front-side bus connections to each socket in a 2P system, as well.

The tradeoffs are several. The 5100 MCH is limited to a maximum of six DIMMs per system and 48GB of total memory, versus 16 FB-DIMMs and 64GB total memory for Bensley. Also, the 5100 MCH's two channels of DDR2-667 memory yield a peak of 10.6 GB/s of bandwidth, compared to Bensley's 21 GB/s max.


The guts of our San Clemente test rig, fully populated with six DIMMs

Our San Clemente test system underscored its memory capacity limitations by proving to be incompatible with our 2GB DDR2 DIMMs, for whatever reason. We were limited to testing with only 6GB of total memory by populating each of its DIMM slots with 1GB modules.

Since AMD's 45nm Opteron HE products aren't out yet, the closest competition we have to the Xeon L5430/San Clemente combo is the Opteron 2347 HE, a 65nm part with a 55W ACP (68W TDP), a 1.9GHz core clock, and a 1.6GHz north bridge/L3 cache. That's a rough comparison for AMD, but things should change once the 45nm Opteron HE parts arrive next quarter.

At the other end of the spectrum entirely is the Xeon X5492, an ultra-high-end processor (nearly $1,500 list) that tests the outer limits of Intel's 45nm process tech with a 3.4GHz core clock, a 1600MHz FSB, and a 150W TDP rating. We've tested a pair of these babies on the Stoakley platform. Stoakley is essentially an updated version of the Bensley platform with higher bandwidth, but it's been targeted largely at workstations and HPC systems.

There really is no Opteron analog to the Xeon X5492. The closest comparison might be to the 65nm Opteron 2360 SE, which has a 105W ACP (and 119W TDP), but Shanghai has higher clock frequencies and a larger cache in a much smaller power budget, so the 2360 SE is essentially obsolete. Again, we may have to wait for the introduction of 45nm Opteron SE models before we have a truly comparable product from AMD—and even then, AMD may choose not to produce an Opteron with a 150W thermal envelope.