Original URL: http://www.theregister.co.uk/2007/02/11/amd_enhanced_powernow/

AMD's 'Barcelona' cuts power one core at a time

Getting coarse with Intel

By Ashlee Vance

Posted in Servers, 11th February 2007 23:21 GMT

AMD's elaborate and lengthy four-core processor striptease continues this week with some geeky revelations around power saving technology. At the ISSCC (International Solid State Circuits Conference) in San Francisco, AMD will talk up "Enhanced PowerNow!" – the latest iteration of its power tweaking technology due to appear in the four-core "Barcelona" version of the Opteron chip.

While the PowerNow! tools in today's Opteron still warrant an !, according to AMD, the Enhanced tools are altogether more fantastic. Most notably, the technology makes it possible to control the frequency and power of each core individually.

"What we have today with the dual-core Opteron and PowerNow! is nice," Brent Kerby, AMD's Opteron product manager told us. "We show up to a 75 per cent power savings at idle.

"The limitation is we can only lower the performance state to the highest utilized core setting no matter what's happening with the other one. With the Enhanced PowerNow!, you can tweak each core to deal with the demands of a software workload."

In addition, AMD has made it possible to run the memory controller at full speed while powering down the CPU cores. This lets the overall chip keep memory performance high while lowering the energy consumption of the cores. AMD claims that Intel will struggle to match such technology due to its multi-chip-module packaging used to produce four-core Xeons.

Customers in the high performance computing market who run their systems all out, all the time will only be mildly impressed by the Enhanced PowerNow! technology. But business customers running their server at well below 60 per cent utilization should see some dramatic reductions in energy costs.

AMD has proved reluctant to provide exact savings figures around the new technology, leaving us with little more than a promise that it trumps what Xeon has to offer. The chipmaker, however, has been more upfront around Barcelona's overall projected performance, claiming the chip will beat comparable Xeon's by 40 per cent on a wide set of benchmarks when it ships later this year.

Back to the power management, AMD will also use ISSCC to discuss a revamped memory controller that can turn off Read or Write logic when it's not needed. "If you're doing a lot of Writing, then the chip can shutdown the Read logic and vice versa," Kerby said.

AMD has also embraced fine and course clock gating with Barcelona. With the coarse gating, AMD can shut down larger chunks of transistors, while the fine grained gating shuts down a smaller number of transistors. Both techniques provide significant power savings, according to AMD.

We can't wait to see how many more Barcelona details AMD can squeeze out in the coming months. With overall performance, socket-compatibility, packaging and power savings behind it, AMD will likely turn next to cheering Opteron's role in powering Second Life sex shops. ®