Shake it all about: Economist

How to use your laptop to locate an earthquake

IF YOU drop your laptop computer, a chip built into it will sense the acceleration and protect the delicate moving parts of its hard disk before it hits the ground. A group of researchers led by Jesse Lawrence of Stanford University are putting the same accelerometer chip to an intriguing new use: detecting earthquakes. They plan to create a network of volunteer laptops that can map out future quakes in far greater detail than traditional seismometers manage.

Seismometers are large, expensive beasts, costing $10,000 or more apiece. They are designed to be exquisitely sensitive to the sort of vibrations an earthquake produces, which means they can pick up tremors that began halfway around the world. By contrast, the accelerometer chips in laptops, which have evolved from those used to detect when a car is in a collision and thus trigger the release of the airbags, are rather crude devices. They are, however, ubiquitous. Almost all modern laptops have them and they are even finding their way into mobile phones. The iPhone, for example, uses such a chip to detect its orientation so that it can rotate its display and thus make it easily readable.

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Thanks for the memory: Economist

A mathematical trick may allow people to scatter their computer files across the world's hard disks

IF YOU have lots of unused storage space on your hard disk, then why not share it with others on the internet? The benefit could be distributed storage for your own files, making them available any time via the web, even if you are nowhere near your computer—indeed, even if your computer is switched off. That desideratum is what a Zurich-based firm called Caleido is aiming to provide, with a free online storage service known as Wuala that was recently introduced to the public.

Though the idea underlying it is simple, Wuala requires some nifty technology to make its distributed system work reliably. In particular, its developers, Dominik Grolimund and Luzius Meisser, have used a clever mathematical trick to compensate for the fact that the participating computers will come and go from the internet in an unpredictable way.

The challenge is how to minimise the number of copies of the same file that have to be distributed. Copying costs participants both storage space and bandwidth. Yet there have to be enough copies to ensure that there is at least one available most of the time. If, for example, each computer is online 25% of the time, then a quick calculation shows that you would have to copy each file to 100 different computers to ensure that 999,999 times out of a million there is at least one copy available when a user looks.

For more on this article, please click on the following link: Thanks for the memory: Economist