Everybody knows Linux as an open-source operating system - available today for many different hardware architectures - which has become the de facto alternative to the Redmond’s product, especially in the servers segment. Linux versus Windows, Windows versus Linux: this diatribe on which of the two is the best solution has been literally filling most of the computer forums and computer magazines. We are not going to add some fire on that already “hot” discussion, but rather analyze some real facts and take the appropriate conclusions.

First of all, we are talking about supercomputers, those machines with very high performance level used in many research laboratories, universities, military sites and govern agencies. Supercomputers are also called as HPC, acronym for High Performance Computer, and have always been characterized by being able to execute a huge number of floating point operations in a second. There are many applications where supercomputers are used: weather forecast, simulation of nuclear reactions (and also simulation of nuclear weapons), cryptography, molecular and biological modeling and simulation, aerodynamics (used both for automotive and avionics applications), market researches, and so on. HPCs are very common today and their costs have become affordable for many, mainly due to the fact they are built using off-the-shelf hardware: instead of designing custom chips (expensive and not easily reusable), HPCs are today created using top-level processors, such as the AMD Opteron 64-bit or the Cell Broadband Engine.

On the web there is an important and useful site (www.top500.org) which started in 1993 and ranks the top 500 supercomputers in the world. Their statistics are usually updated twice a year (the latest data refers to June 2009) and you can easily navigate among the data by selecting some fields such as: the vendor, the performance, the operating system, the operating system family, and so on. For instance, the newest rank says that the fastest HPC in the world is the IBM Roadrunner, an hybrid machine based on clusters of AMD Opteron and PowerXCell 8i (yes, it is derived from the original chip which has been designed for videogame consoles and installed on the Sony Playstation 3): it features a performance superior to 1 petaflops (1 petaflop corresponds to 10^15 floating point operations per second). The IBM Roadrunner is not only extremely fast, but it is also designed to achieve an efficient level of power consumptions. In fact, it has also a top place in the Green500 ranking, which lists the supercomputers according to their performance - power consumption ratio: that is a very important aspect, since supercomputers require many megawatts for their functionalities and a lot of heat must be dissipated, too.

Another important aspect to be noticed is that the operating system which controls the IBM Roadrunner operations is based on Linux; actually it is called RHE, that is the acronym for RedHat Enterprise Linux. What happens for the IBM Roadrunner is not uncommon, and, basing on the data reported by the Top500 site, we can say that most top level supercomputers have a variant of Linux as operating system. In other words, we can say that supercomputers love Linux! Going through the Top500 list filtered by operating system, the results are literally surprising:

• all the first 10 supercomputers in the ranking are using Linux or some variant derived from it. Cray, for instance, uses CNL (Compute Node Linux) which is a light Linux kernel targeted for multiprocessor architectures
• 19 of the top 20 supercomputers have Linux as operating system
• Linux has an 88.60% share on the whole top 500 supercomputers

The top 20 rank is as follows:

It is now clear the top 20 supercomputers manufacturers (IBM, Cray, and SGI) have preferred Linux with respect to other operating systems. Why that happened? IBM has been using Linux since 2002, when a former top level supercomputer (BlueGene) was developed. According to IBM, Linux has been choosen because it is open and it can be extended to run a BlueGene (or Roadrunner) class machine. Moreover, Linux has behind a huge community working all over the world and they can provide valuable support, feedbacks and suggestions.
The operating system family share rank is as follows:

The following image shows the IBM Roadrunner supercomputer:

Reference

www.top500.org
www.green500.org