Linux Rules Supercomputers

The homegrown Linux operating system has come a long way from its origins as a college kid's pet project and computer hobbyist favorite. Refined in recent years by professional computer programmers at IBM , Hewlett-Packard , Novell and Red Hat , Linux now has become so technically powerful that it lays claim to a prestigious title--it runs more of the world's top supercomputers than any other operating system.

A group that keeps track of the top 500 supercomputers in the world estimates that Linux powers 60% of those machines, displacing Unix, which used to be the most popular operating system for high-performance computing.

The official Top 500 list, available at www.top500.org, does not contain operating system statistics. But the scientists who maintain the list privately keep track of what operating systems are running on the computers, says Hans Werner Meuer, a computer science professor at the University of Mannheim, in Germany, who has been publishing the Top 500 list twice a year since 1993.

One caveat: Meuer says (via e-mail) that his statistics are only an estimate, since some supercomputer Web sites won't report what operating system they use.

"There are many classified and commercial sites where we have to guess which operating system they are using," says Meuer, who is also managing director of Prometeus GmbH, a consulting firm in Daisbach, Germany, that hosts the Top 500 list.

So Meuer may be off by a few machines. Even so, Linux clearly is by far the top choice for high-performance computing. Meuer reckons Linux powers 301 of the 500 top machines, compared to 189 on Unix, two on FreeBSD, a Unix variant, and one on Microsoft 's Windows. (Seven machines are categorized as "other.")

"Linux has dominated the marketplace for high-performance computing," says Mark Seager, assistant department head for advanced technologies at the Lawrence Livermore National Laboratory in Livermore, Calif., which operates ten machines on the Top 500 list, including Blue Gene/L, the world's most powerful supercomputer, and Thunder, which ranks fifth.

Both of those machines run Linux, as do several other Lawrence Livermore supercomputers. Lawrence Livermore shifted to Linux a few years ago as an alternative to AIX, the IBM version of Unix.

Seager says the lab chose Linux partly because it is "open source," meaning users can change the code to suit their needs. Also, they can use Linux without paying a licensing fee.

Moreover, Seager says Linux outguns popular Unix operating systems like AIX and Solaris from Sun Microsystems because those systems contain features that make them great for commercial users but add a lot of system overhead that ends up limiting overall performance. One example: a "virtualization" feature in AIX lets many applications share the same processor but "just hammers performance," Seager says.

Linus Torvalds Linus Torvalds , who created Linux in his college dorm room in 1991, says (via e-mail) that Linux has caught on in part because while typical Unix versions run on only one or two hardware architectures, Linux runs on more than 20 different hardware architectures including machines based on Intel microprocessors as well as RISC-based computers from IBM and HP .

"Of course, of those 20, only a handful are relevant for high-performance computing, but it's still a big advantage," says Torvalds, who oversees Linux development from the Open Source Development Labs, a non-profit organization in Beaverton, Ore. "Linux is easy to get, has no licensing costs, has all the infrastructure in place, and runs on pretty much every single relevant piece of hardware out there."