I stumbled upon a transcript from a very recent Science magazine interview with HPC luminaries Jack Dongarra (University of Tennessee, Oak Ridge, Top500 list) and Horst Simon (Deputy Director, Lawrence Berkeley National Lab.) The topic? Nothing less than the future of supercomputers. These are pretty good guys to ask, since they’re both intimately involved with designing, building, and using some of the largest supercomputers to ever walk the earth.

The conversation, transcribed into a chat format, focused on the biggest challenge to supercomputing: power consumption. We can’t simply scale today’s petascale systems up into exascale territory – the electrical demands are just too much. The current top super, ORNL’s Titan, needs a little more than 8 megawatts to deliver almost 18 petaflops. If we scaled Titan’s tech to exascale (which means growing it by 18x), we’d see power consumption at a whopping 444 megawatts – which, if you could even get it into the building, would cost something like $450 million per year at current rates.

We’ve often heard that exascale systems will need to come in at 20 megawatts or less in order to be somewhat affordable. While the evolutionary improvements in power consumption have been significant over the last several years, they won’t be nearly enough to get us into that 20MW power envelope. In the interview, Jack and Horst talk about how we’re going to need some revolutionary technology (they mentioned stacked memory and optical interconnects) to get us to a point where we can even talk about firing up an exascale system.

Power consumption is only the first, and highest profile, problem. They say we’re going to need to see changes – even breakthrough – on several fronts, including operating systems, applications, and even algorithms in order to bring exascale home. And breakthroughs aren’t free, nor even very cheap. Simon said that a “complete exascale program” could cost an additional $300-$400 million per year for 10 years –  over and above what is being spent on HPC now.

Given the current economic climate, it isn’t surprising to learn that funding, at least from Western nations, isn’t hitting these levels. Which is why neither of these HPC authorities is betting on exascale by 2020.

There’s plenty more interesting discussion in the interview. They hit on China’s changing role in HPC; the benefits of exascale; the way HPC technology trickles down into even consumer products; and they answer a number of user-submitted questions. It’s well worth a read.