Down To The Wire: Watts Better About AMD CPUs?

With the launch of the quad-core Opteron processor, AMD aims to change how the market thinks about CPUs. Until recently, the primary message behind selecting a CPU was performance; specifically, how fast the CPU was.

With Barcelona, the message behind the technology is starting to evolve into something seen in the automotive market: performance vs. economy. With automobiles, it clearly breaks down to higher performance equals fewer miles per gallon.

AMD's comparative message now breaks down to performance vs. energy required. In other words, higher processing speeds need to be balanced against watts used. That solidifies the new metric for judging CPUs: performance per watt.

Even so, everyone wants to know how well Barcelona performs and those who have waited for the arrival of AMD's next-generation CPU won't be disappointed. The CRN Test Center was provided with an engineering sample server equipped with dual Barcelona CPUs and 16 Gbytes of RAM.

The server was a rack-mountable 1U unit and was built around a Tyan motherboard, with a beta version of the BIOS for supporting two quad-core AMD Opteron processors.

As tested, the server was configured with Windows 2003 Server. Test Center engineers focused on evaluating CPU performance using a subset of PassMark's Performance Test version 6.1. PassMark's product can test a number of elements in a system, ranging from hard drive to video to optical drive performance. Users of the testing suite can selectively test components, in this case, CPU performance. The software provides an overall CPU-Mark score, which is an averaged composite of scores for integer math, floating point math, prime number find, SSE, compression, encryption, image rotation and string sorting.

The system tested offered a CPU-Mark score of 4693, the highest score the Test Center has seen to date for a dual CPU server. For reference, the Test Center dug up some previous CPU-Mark test results for other servers. In those tests, a dual CPU Intel Xeon 5160 (3 GHz) scored a 3547 and a dual-CPU dual-core AMD Opteron 2218 scored a 2615. When it comes to pure CPU performance, odds are that an Intel Xeon E5345 (2.33 GHz) in a dual-CPU configuration will outperform AMD's 2-GHz quad-core Opteron.

While initial tests show that Barcelona is no slouch, there's a lot more here than just performance. First off, Barcelona is socket-compatible with the dual-core Opterons. Both processors use AMD's socket F(1207) design. What's more, the thermal load of the quad-core CPU is roughly the same as the dual-core Opteron, which means that the same heat sinks and cooling fans can be used, as well as the same power supply. Simply put, you can upgrade a dual-core Opteron to a quad-core with little more than a BIOS upgrade.

AMD has also incorporated some new technologies that increase the efficiency of Barcelona. Case in point: AMD's Cool Core technology, which automatically turns off parts of the CPU, such as the floating-point unit, when not in use. AMD has also enhanced its PowerNow technology, which controls the MHz assigned to each core. In the past, all cores would run at the maximum MHz needed by a single core to complete a task, even if the other cores were idle. The new PowerNow technology allows each core to run at its own MHz load, which reduces power consumption and ties power used more directly to processing power needed.

With Barcelona, AMD is also sticking to DDR2 memory. The company claims that DDR2 uses much less energy than FBDIMM memory. AMD's own tests show that 8 Gbytes of DDR2 memory uses 36.94 watts under full load, while 8 Gbytes of FBDIMM memory uses 101.2 watts under an equivalent load. Further, the same DDR2 memory uses only 14.32 watts when idle, while the FBDIMM modules consume 83.34 watts in the same state. Not only does AMD's choice of DDR2 contribute to power savings, the technology will also reduce the amount of heat that's generated.

When it comes down to it, Barcelona is a welcome addition to the CPU choices flooding the channel. While AMD's new CPU may not be the end-all when it comes to raw power, the CPU's power-sipping ways and backward compatibility with dual-core Opterons will surely create opportunities for channel players in the server market.