Platform Trends: Quad-Core AMDs At Last

AMD has historically introduced new processor technology in the server segment before the desktop or mobile markets. Enterprise IT managers are always looking for faster, cooler, or otherwise better chips, and any company is glad to curry favor with the all-important, volume-buying corporate market.

Last week's release of AMD's long-awaited "Barcelona" core followed this tradition -- and the more important path, AMD says, of creating a true quad-core processor instead of going for the quick fix by pasting a couple of dual-core CPUs onto a single die. This may bring the heavy cost of missing ship dates (can you say "six months late"?), but it offers advantages in other areas.

Quintessentially Quad-Core

Intel's current corporate quad-cores, the Xeon 5300 series for two-way and 7300 series for four- and eight-way servers, are technically dual-dual-core CPUs. Putting two processors on the same package requires concessions in terms of interprocessor communication, resource duplication, power savings, and overall performance. By contrast, Barcelona -- officially known as the third-generation Opteron -- is what AMD calls a native quad-core design.

The new Opteron represents AMD's first foray into 65-nanometer-process, quad-core processing. The CPU contains 64K of Level 1 and 512MB of full-speed Level 2 cache per core, along with 2MB of dynamically shared Level 3 cache. Barcelona offers notable improvements over past AMD designs, including the doubling of many internal data, instruction, and cache pathways.

This is a huge advantage when it comes to internal processing, as is the fact that the integrated memory controller is physically dual-channel, and able to handle 64-bit read and write transactions simultaneously, rather than just doubling available bandwidth for one-way transactions. The built-in memory controller has also undergone revisions, with improved prefetch mechanisms and larger onboard buffers.

The nine new CPUs that make up the Opteron 2300 and 8300 series -- for two- and eight-way systems, respectively -- span clock speeds from 1.7GHz to 2.0GHz. Energy conservation- and cooling-minded buyers can choose among four 75-watt and five 55-watt models. Prices for the 2300 series range from $209 to $389; for the enterprise-oriented 8300s, from $698 to $1,019.

The Opteron 2300s' prices look quite low for an (a.) new and (b.) quad-core part, but AMD expects to increase clock speeds (and potentially prices) right out of the gate. The 2300 series processors are also physically a bit different from the usual AMD design, with beveled edges that make them look more like Intel CPUs than previous AMDs. This is supposed to ensure better linkage with the heatsink/fan and provide enhanced cooling overall, but it still looks like an ode to Intel R&D.

The quad-core Opterons continue to support AMD's Socket F package, so existing workstation and server platforms will be able to seamlessly upgrade to a newer, faster, and more efficient processor. In most cases, this should require merely a BIOS update, with no change to existing motherboards, enclosures, memory, or even cooling designs.

This is night and day from Intel's practice of changing platforms as often as underwear, introducing a new chipset, bus speed, or form factor with each new CPU revision and offering little or no compatibility with older platforms. While desktop users certainly benefit from the availability of drop-in upgrades, the latter are potentially even more valuable in the server market. Hardware and manpower costs are higher, and downtime more risky, so the prospect of simply adding new Opterons to an existing server base will be an attractive prospect for many CTOs.

A Mixed Bag of Benchmarks

Barcelona's larger processor bus and greater memory bandwidth pay off in a wide range of server tasks, helping the third-generation Opteron perform extremely well in memory-intensive benchmarks. Memory and cache latency scores aren't quite as good, and this may be due to the addition of a slower Level 3 cache. The presence of dynamically shared Level 3 cache can certainly pay off in many ways, but does come at the cost of increased latencies.

In terms of CPU-specific benchmarks, AMD's quad-core offers a huge performance advantage over current dual-core Opterons, but only a small portion of this is based on core-to-core improvement. In the server environment, where multithreaded software is the norm, quad-core will always outperform dual-core, and that's where most of the advantage lies.

As far as challenging Intel's quad-cores, it's more of a mixed bag, especially with the fastest quad-core Opteron running at 2.0GHz and the fastest quad-core Xeon at 3.0GHz. For now, AMD has failed to deliver a slam dunk: Overall power and thermal scores are extremely good for the new processor, but it still trails in several important server benchmarks.

Performance-per-watt is an important part of the Opteron Barcelona marketing plan, as is AMD's newly proclaimed the Average CPU Power (ACP) metric. This measures power consumption of the processor cores, memory controller, and HyperTransport links while running a series of typical workloads. As an alternative to the simpler, familiar TDP (thermal design power) scores, ACP looks to be AMD's way of highlighting the potential power-saving advantages of the new platform.

Related enhancements include AMD CoolCore Technology, which turns off unused parts of the core, and a couple of dynamic core features: Independent Dynamic Core Technology enhances AMD's PowerNow by allowing each core to change its clock speed independently, while Dual Dynamic Power Management provides each core with an independent power supply, letting it operate on different voltages.

Precursor to a Phenom

The Barcelona core is a promising introduction to AMD's new 65-nanometer quad-core architecture, and it bodes well for the upcoming Phenom desktop version. Power and thermal specifications are excellent, and the use of Socket F (and Socket A) will make AMD a hero to many cost-conscious buyers.

The emphasis on performance-per-watt is both promising and risky, as businesses do care about power costs, but the choice does make AMD seem timid or scared about matching pure performance benchmarks with Intel. Still, while it doesn't outpace the quad-core Xeon, Barcelona delivers competitive speeds with higher per-clock processing. The biggest achievement of the 2.0GHz quad-core Opteron? Making desktop enthusiasts salivate for a 2.6GHz Phenom.