"For some apps where you don't have that dependency the number could be smaller," he said. "ARM's an interesting thing to look at and, if nothing else, if it lights a fire under Intel and AMD to deliver more effective x86 solutions, I'm happy."
Microsoft said recently it would port Windows to ARM processors for use in mobile devices such as tablet computers. But that's different from PCs and servers, Bhandarkar argued, which are expected to run a wide range of existing software.
ARM, which is developing a more powerful chip design for servers and switches, is more optimistic. It notes that some servers need to run only a handful of programs, such as the Lamp stack (Linux, Apache, the MySQL database and PHP).
Gwennap too said ARM processors could play a part in data centers. And while they are likely to be used initially by large Internet companies and collocation providers, they may also be used in the enterprise for some applications.
"Clearly software is a big barrier, but some customers are willing to work with that," he said. "It's going to be a longer-term thing, but if ARM can get established in large data centers first and then migrate to enterprise applications, there could be some momentum there."
An Intel spokesman noted that HP sells a home media server with an Atom processor, but Intel has "no announcements to make" regarding Atom chips for data centers, he said.
He also noted that Google and Microsoft have, in the past, argued in favor of more powerful chips. "[A]lthough we're enthusiastic users of multicore systems, and believe that throughput-oriented designs generally beat peak-performance-oriented designs, smaller isn't always better," Google wrote in a research paper last year.
But Bhandarkar said there are diminishing returns in moving to chips with more cores and higher clock speeds, at least for Microsoft. The company looks at performance per watt per dollar when choosing hardware, and the performance gains from beefier chips don't make up for the increase in power use, he said. "So in many of our configurations, we only populate one socket with a quad-core" processor, he said.
Processors are just one part of the energy-efficiency equation for Microsoft, which looks at its data centers holistically. It provides server makers with fairly strict specifications and asks them to compete for its business.
It has installed servers with no fans, for example, moving them to the rack level instead for greater efficiency. It also specifies servers with no CD or DVD drive, fewer DIMM slots and PCI cards, and power supplies rated to the Gold or Platinum standard by the Climate Savers Initiative.
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