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Strong points of Linux as supercomputing tool

Nowadays, Linux is the best operating system to do supercomputing, high-availability uses or high-performance uses with low budget.

• Existence of free Fortran 77 compilers. The most of the scientific libraries are in Fortran, and the most of the scientific programs are also in Fortran, due to historical reasons. Most of the computational chemistry programmes are written in Fortran, and nobody at this moment is thinking about porting the gigantic QCPE dinosaurs-packages to C.
• Existence of free C compilers. C is fast and cool. And today there are lots of people developing code using C.
• Stability. A real calculation on computational chemistry problem need lots of time to be completed. Some problems, like folding problems, are especially CPU-intensive. If the machine hangs all day, you can not use the machine for serious research. Linux is really stable, and that thing allows you to do long simulations on your PC desktop.
• Performance. Many workstations are known for the low user time response. A cheap PC may need 40 minutes of CPU, but you wait only 45 minutes. A AIX workstation used by M.D. students, Ph.D. students, postdocs, researchers, will need 15 minutes of CPU, but you will wait a couple of hours. Final performance is better.
• Availability. All of us have a PC on our desktop. Few of us has an parallel supercomputer on our desktop. Anyway, if you want the supercomputer and you have the money, you should wait long customs delays and taxes. You can buy just-in-time a PC on any store, and maybe your work will delay more, but it will be finished before the supercomputer is here.
• Availability of PVM. There exists a complete and efficient implementation of PVM library. PVM is free and well-documented, and it is available as Debian, RPM and tallball, with lots of free documentation and its wrappers to Fortran. Some Linux distributions include PVM -SuSE, RedHat PowerTools, Extreme Linux project-. Usually it is easier to recompile a parallel package for a pile of cheap Pcs with Linux without native support and documentation, than recompiling the same package for a supercomputer.
• Availability of MPI. As on the case of PVM, there exists lots of applications that make use of MPI and that can be directly recompiled under Linux. MPI's situation is completely different than PVM's one. On PVM we had only one full implementation. On MPI, we have some different implementations. All of them use to work fine under simple applications; but some applications can need features for which a determined implementation lacks of support. The four most common free implementations of MPI standards are MPITCH, LAM, CHIMP and UNIFY. Unify is somewhat special. It is a PVM wrapper for MPI calls, that allows as emulate a MPI as mix PVM and MPI calls on the same code.
• Supercomputing facilities. Finally, Linux have some supercomputing facilities. The most important but less appreciated is that Linux support most of Intel-based multiprocessor motherboards as part of the stable line of Kernels. But this facility is not the only one. We have two cheap-supercomputer projects, Beowulf project -from CESDIS, NASA- and Mosix project -from the Hebrew University of Jerusalem-. The two ones use completely different points of view.
• Optimal MIPS/$. The most important one. Ask for the price of a Linux box. Ask for the price of a supercomputer. Look for the cost for MIP. Only as a example, we can see the table that come with this article. Other example: The last 9 of March of 1999, on LinuxExpo 1999, Beowulf class supercomputers outperformed to Cray supercomputer. The mundial record of PovRay -an important ray tracing application, that involves heavy floating point calculations- benchmark, hold by a Cray processing T3t-900-AC64 of $5.5 million, was broken by a Beowulf class supercomputer of $150,000. The Beowulf cluster rendered the image three times faster that the Cray supercomputer. There are hundreds of other examples.

There exists other advantages, but form part of the advantages of Linux and Free software. Price of hardware, spare parts and reparations, on-line support, global quality... Sure you know lots of them.

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