Processors based on the x86 architecture are getting to as low as 2 or 3 watts per core, he said. Reducing the power of the CPU any further doesn't make sense when taking into account the power needed to run the other components in a server platform, such as the I/O and memory, he argued.
"I don't think the math makes sense," he said.
Add to that the overhead of trying to virtualize and manage a data center with a mix of ARM and x86 servers, and ARM makes even less sense. "The cost of heterogeneity in a cloud computing model is very high," he said.
Applied disagreed. Gelsinger's argument holds true for traditional x86 servers that have their own individual chassis, power and cooling supply, but the industry is heading toward a shared infrastructure, and even shared components such as I/O and memory, said Gaurav Singh, Applied's vice president for engineering and product development
"In the new systems, the math makes a lot more sense," he said.
Analyst Nathan Brookwood of Insight64 sided with the ARM camp. "Why I believe ARM makes sense is because it allows you to innovate at the CPU-level in a way that you can't with x86, because Intel and AMD are the only guys who have access to those cores," he said.
Applied, by contrast, was able to build a highly integrated SOC by innovating around ARM's CPU core.
SeaMicro, the server startup bought this year by AMD, has been selling even denser servers than Applied is proposing, based on Intel's Atom and Xeon processors. But SeaMicro had to use a two-chip solution, with its networking fabric on a separate piece of silicon, because it couldn't modify Intel's chips, he noted.
Now that it owns SeaMicro, AMD has hinted that it will integrate the company's technology onto its own Opteron server chips. "But that's a couple of years away," Brookwood said.
Gelsinger isn't an unbiased observer, of course. In two days he's scheduled to take over as CEO of VMware, which is mostly owned by EMC, and VMware has built its business on the x86 architecture. It's software, at least for now, does not virtualize ARM servers.
But while Gelsinger has serious doubts about ARM, he's apparently not religiously opposed to it. "If they emerge, if they're really good, of course we'll make our software support them as well, but I'm very skeptical," he said.
Sign up for CIO Asia eNewsletters.