Hardware .. Travel: Supercomputer in Potsdam, Germany at PIK.

What exactly does a supercomputer look like? What might it do? If you let your imagination run wild perhaps you picture a small sphere suspended in a liquid emitting a strange ethereal light. It's only visible by video as it is hidden below the ocean floor ... or perhaps you picture a big black box, or even a series of black boxes ... in a building next door.

The Approach

We went to the Potsdam Institute for Climate Impact Research to see for ourselves. Potsdam is a half hour by double-decker train from Berlin (or an hour if you take the stop-everywhere local S-Bahn train). It's a nice ride through pretty woods and past lakes which are popular places to visit for Berliners.

Once at Potsdam Hauptbahnhof (main station), the institute is a 15 minute walk up Albert Einstein strasse. He lived in the area for a time and taught at Berlin's Humboldt University. On the campus grounds there is a modernist observation tower, designed by Erich Mendelsohn, which was named after him as well.

The Campus

But that's getting ahead of ourselves. The campus is quiet and leafy and with a mixture of scattered buildings. We walk up a winding lane looking for building A31 and find a grand brick building with tile inserts and two astrophysical observation towers which was built in the late 1800's. Here is the headquarters of the Potsdam Institute for Climate Impact Research (PIK in German) and we seek Karsten Kramer who looks after the computer centre.

Here, from their website ( is a statement of what they do. 'PIK addresses crucial scientific questions in the fields of global change, climate impacts and sustainable development.

Researchers from the natural and social sciences work together to generate interdisciplinary insights and provide society with sound information for decision making.

The main methodologies are systems and scenarios analysis, quantitive and qualitative modelling, computer simulation, and data integration.'

The Computer Centre

A few years ago they faced the problem that the computing resources needed to be expanded and there wasn't space available. Just plonking another building down wasn't an option because although there's certainly enough space, there are strict planning rules that apply. The solution was to build an underground facility right next to the main building.

And that's where we headed next. The picture below shows the building. The flat, grassed area is the top of the centre.

There are security precautions, and once these are attended to we enter the hallway of a several roomed bunker with concrete walls painted white. Just as you'd imagine, the space is spotless and there is an absence of stacks of do-dads and bits that might be useful sometime. There is a hum from the fan room which moves 20,000 cubic metres of air an hour in order to keep all those CPU's cool. Also in that room are rows of cylinders for the fire extinguishing system. These cost 20,000 Euros to fill. The electricity bill doesn't bear thinking about.

The Machinery

In another room are the tape drive backup machines. There is half a PetaByte of storage here with each tape row being able to take 500 GBytes at a read rate of 85 MBytes per second and a write rate of around 65 Mbytes per second. While tape drives are old technology, these drives are fairly new and represent quite advanced technology. They are more efficient in power use than harddisks and not much different to DVD burning in power use. The DVD loses in storage capacity however.

Next is the computer room itself which includes the webserver for the PIK website. If you clicked on their URL above, you would have virtually visited this room. The webserver is, of course, not the most interesting machine in the room.

When this centre was opened, IBM was contracted to supply 200 x Power-3 IBM SP-2 which was to be upgraded to a 240 x Power-4 cluster. This was delivered at the start of 2003 and gave the centre a rank of 142 on the list of the world's 500 most powerful computer systems. The cluster's measured performance was 575 GFlop/s with a theoretical maximum of 1.056 GFlop/s.

The newest big iron to arrive came on the last day of 2006 is a Linux cluster.

This is a 224 processor cluster and is arranged in four blade centres with 14 blades each. Each blade has two dual core 3GHz Intel Woodcrest CPU's and 8 GBytes of RAM. The nodes are diskless and boot Suse Enterprise 10 Linux. There is also temporary storage of data on 70 TByte high performance parallel filesystem which is connected to the blades by an Infiniband network.

Below are photos of an individual blade, closed and open. On the right, in the opened blade, can be seen the two dual core CPU's and next door can be seen the RAM.

We were interested in how jobs get allocated on this system and also how they actually work the machine. Might, for example, the system operate a little like SETI at home where the number of CPU's available ebbs and flows? In fact the number of CPU's is booked for any given job and these jobs can run for one, seven, or thirty days. 'Only the (automatically calculated) priority of jobs depends on which of the three classes (1,7,30 days) a user had selected (priority to get scheduled for short jobs being higher of course)'. Another aspect is that a lot of the calculations are iterative and thus not particularly suitable to using a mass of CPU's in parallel.

More photos and information can be seen at PIK's photo album page at

After looking in the centre we went for a wander further around the campus and the saw the Einstein tower and, amongst other things, a glass-walled bike shed with silhoettes of birds applied to stop birds flying into the glass. We also found a cafe where we had a huge lunch for about the same price as a muffin and coffee at the local train station.

The campus is open to the public.

Thanks to Karsten Kramer and Ciaron Linstead.

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