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AMD's Opteron 254 processor

Single core's not dead yet

FOR THE PAST 12 months, Intel and AMD have praised the merits of their respective dual-core CPU designs and focused on thread-level parallelism as the key to better perfomance, while gradually distancing themselves from the old "clock speed" performance standard. Although Intel beat AMD by a handful of weeks when it came time to formally launch dual-core desktop systems, AMD was the first company to offer dual-core solutions across the server, workstation, and desktop markets.

With dual-core CPUs firmly established, neither manufacturer has been talking much about single-core processors in the workstation market—but the high-end single-core processor still has a hand or two to play before it makes a final exit. AMDÂ’s recent stealth launch of the Opteron 254 at 2.8GHz ensures that the limelight stays focused on their dual-core products, while the Opteron 254 offers an intriguing option for buyers caught on the fence between lower-speed, dual-core and higher-clocked, single-core processors.

At $851 per chip, the Opteron 254 is positioned well above the Opteron 265 (1.8GHz dual core) at $690 and directly opposite the Opteron 270 (2GHz dual core) at $851. The Opteron 275 and Pentium Extreme Edition 840 top out at roughly at $1000 each, and the Xeon 3.6GHz is actually the cheapest of the processors we compare here, at only $690 per core. There's not much new to talk about when comparing the price-to-performance ratio of a single Opteron 254 against a dual-core Opteron 270. In applications or test suites that are primarily or entirely single-threaded, the 254 would stomp the dual-core processor. In applications or suites that favor multi-threading, the dual-core processor would return the favor, with an added helping of creamy smoothness as an additional purchase incentive.

When we start talking about 2P vs. 4P, however, things get more interesting.

The Opteron 254

Why two is sometimes better than four
AMD and Intel may have declared that thread-level parallelism and dual-core CPUs are the future of computing, but the software transition required in order to make such claims ring true will be anything but quick and painless. Until Intel launched Hyper-Threading in 2002, there was little to no reason to create multi-threaded desktop software, since no desktop CPUs could take advantage of it.

The proliferation of Hyper-Threaded CPUs gave desktop-oriented software companies an incentive to implement multi-threading—but only to a point. There are a number of applications we could refer to as strictly dual-threaded, or, in some cases, what I call "minimally multi-threaded". The latter term refers to programs that were designed with Hyper-Threading in mind, and deliver the same 10%-20% speed boost whether they are run on a dual-core or Hyper-Threaded CPU.

The advent of dual-core products gives the software industry new reason to optimize mainstream products for multi-threading, but the cost and effort required to do so can be significant. Generally speaking, the more parallel the code, the more difficult and time-consuming it is to create. Spin off enough threads, and you'll inevitably begin to create other bottlenecks within the system, the sum total of which could actually degrade performance. As impressive as a dual-core, dual-CPU system is on paper, thereÂ’s no guarantee that an application billed as "multi-threaded" will actually take advantage of all four cores. Even if it does, quad-core support isn't an inherent guarantee of scalability. Several of the applications we'll examine today are capable of using all four cores in a quad-core system, but don't demonstrate anything close to linear scaling when compared to a dual-core system. In such scenarios, the Opteron 254's 27% clock advantage over the Opteron 275 may prove to be more beneficial than the Opteron 275's additional cores.