Exascale supercomputers: Are the world’s most powerful machines operating in secret?

A supercomputer called Frontier has been officially crowned as the world’s first exascale computer – one capable of a billion billion operations per second – but more powerful machines may be out there

By Matthew Sparkes

A new supercomputer called Frontier has been widely touted as the world’s first exascale machine – but was it really? Although Frontier, which was built by the Oak Ridge National Laboratory in Tennessee, topped what is generally seen as the definitive list of supercomputers, others may already have achieved the milestone in secret.

What is an exascale computer, and why is it important?

Exascale is a term used to describe the arrival of machines that can carry out a billion billion operations per second. Exascale has long been a target – as a round number often is – for manufacturers seeking ever higher performance.

Today, supercomputers are vital in carrying out a wide range of scientific research, running large simulations of everything from nuclear physics to the effects of drugs, and even training artificial intelligence models. They are also used to mine data and look for patterns. Having the most powerful machine can give academics, companies or governments an edge.

Who tracks the world’s most powerful supercomputers?

The definitive list of supercomputers is the Top500, which is based on a single measurement: how fast a machine can solve vast numbers of equations by running software called the LINPACK benchmark. This gives a value in float-point operations per second, or FLOPS.

But even Jack Dongarra at Top500 admits that not every supercomputer is listed, and will only feature if its owner runs the benchmark and submits a result. “If they don’t send it in, it doesn’t get entered,” he says. “I can’t force them.”

Why would owners not want to be listed?

Some owners prefer not to release a benchmark figure, or even publicly reveal a machine’s existence. Simon McIntosh-Smith at the University of Bristol, UK, points out that not only do intelligence agencies and certain companies have an incentive to keep their machines secret, but some purely academic machines like Blue Waters, operated by the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, are also just never entered.

Blue Waters project director Bill Kramer said in 2012 that the Top500 list was “interesting at some point, a while ago, but that now in some ways may be doing detriment to the community”.

How could benchmarking be detrimental?

While FLOPS is a useful measure of performance, different machines can be better suited to certain types of task, so LINPACK doesn’t always tell the whole story.

McIntosh-Smith says that the opposite is also true, and that some owners are so keen to get on the list that they will design their machines to be good at carrying out the benchmark rather than the everyday tasks they were built for. “There have definitely been, even recently, systems where you’d say they are compromised in some way or other in order to hit a certain LINPACK score that might mean they’re not quite so good for more generic science – amazing systems that cost hundreds of millions of dollars,” he says.

So how many exascale machines are there?

Dongarra says that the consensus among supercomputer experts is that China has had at least two exascale machines running since 2021, known as OceanLight and Tianhe-3, and is working on an even larger third called Sugon. Scientific papers on unconnected research have revealed evidence of these machines when describing calculations carried out on them.

McIntosh-Smith also believes that intelligence agencies would rank well, if allowed. “Certainly in the [US], some of the security forces have things that would put them at the top,” he says. “There are definitely groups who obviously wouldn’t want this on the list.”