Päivä jolloin Sisunen rakennettiin

The day we built Sisunen

Maria Virkkula

– And what if we use a really high density, what happens then? asks ten-year-old Luukas.

Joona ja Luukas stare intently at the screen. They are trying out a programme that demonstrates the power of Sisunen, a mini supercomputer that is being built in Heureka – The Finnish Science Centre in Vantaa over the weekend.

The programme is simulating liquid. It continuously calculates differential equations for how water or another liquid behaves under the influence of a variety of different forces. As the calculations are divided between different nodes on the screen, the LED lights attached to the side of the units start flashing in an increasing number of different colours. Sisunen is therefore working even faster.  

Luukas is listening intently the introduction with the rest of his group.


The programme is reminiscent of a game, and the boys are clearly fascinated by it. And no wonder. Luukas already knows that he wants to work in IT, just like his dad.

– Can you save this on a memory stick? Luukas wonders, staring at the operations on the screen, and CSC's Systems Specialist Pietari Hyvärinen has to come up with a suitable reply.

Luukas and Joona are two of the supercomputer builders taking part in the opening day of the Sisunen event. Theirs is the third team of the day. The original schedule has been completely revised due to the large number of enthusiastic registrants. Soon, Sisunen will be dismantled again so that the last construction crew of the afternoon can take their turn.

As the calculations get faster, more and more colours appear on screen.

May I present Sisu?

While the eager beavers are busy putting dozens of NUC Mini PC units in place, other visitors have gathered to listen to an introduction to supercomputers given by CSC's experts. They are standing on a work of art – pieces of tape trace the dimensions of Sisu, Finland's most powerful supercomputer and the model for Sisunen (aka Little Sisu): 11 x 1.57 metres. Big Sisu is a bit taller than an adult man – almost 2.2 m.

– A supercomputer is a scientific instrument – just like an astronomic telescope, particle accelerator or spectrometer – that just happens to be built from the same parts as a regular computer. It's not really a computer as such. You don't use it for the same things as you would your home computer. It's meant for a number of quite different uses, such as performing scientific, technical calculations, explains CSC's Senior Application Specialist Pekka Manninen.  

Heureka's floor was taped to show the size of Sisu.


– As you can imagine, one of Sisu's cabinets generates quite a lot of heat. It's like placing a dozen sauna stoves in a cabinet like that and putting them on full power. It generates a lot of heat that must be removed, and that requires its own technology.

However, their power makes supercomputers essential to science. Typical users include university researchers.

– Supercomputers don't exist for their own sake – they need to have a purpose. And that purpose is progress: to crunch enough numbers to take scientists' and researchers' dreams from pen-and-paper methods to working models. 

Visitors were able to play around with parts from old supercomputers.

Although little Sisunen has only a fraction of the power of big Sisu, it is perfectly suitable for demonstrating parallel computing models. Simulations can provide computational answers to research questions that would otherwise require demanding experimental set-ups for empirical research.

Sisunen is good at this. In spite of being only a few hours old, Sisunen's theoretical power is up to 1.5 times that of Finland's most powerful supercomputer in 2006 (IBM p690).  

Art and science

Just over ten metres from where Sisunen is performing its operations, a battle of supremacy is being fought in space. Shooting Star is a physics game in which you compete to control the planets in a star system with the blazing sun burning at your neck.

The remaining space between the rooms has become something of an art gallery. The walls have been decorated with colourful supercomputers designed by visitors.



From this gallery, you can easily watch the throngs of interested people who have visited throughout the course of the day. Experts have been asked knowledgeable questions on topics such as software, languages, and interfaces. And, of course, the age-old question: how old is Sisu?

– The first phase was installed in 2012, while the current configuration dates from summer 2014. Supercomputer technology quickly becomes obsolete. Sisu is already starting to approach senior age, says Manninen.

Lively young Sisunen on the other hand is still blinking its colourful lights as evening begins to fall at Heureka. Saturday's last team of builders have successfully completed their task. Only a few final adjustments are required to the software. A new day with Sisunen and supercomputers lies ahead.


Young scientists listen intently to Oscar Kramer as he explains how to build Sisunen.

Chemistry student Topi Suominen shows visitors how to play Shooting Star.

CSC's Pekka Manninen tells the audience all about supercomputers.

Mini supercomputer Sisunen is ready – now!


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