The fastest supercomputers today have thousands of processors working in parallel, giving a total processing power that is measured in petaFLOPS – quadrillions of floating point operations per second. So, supercomputers are used to run complex models that require huge numbers of calculations every second. For example, supercomputers are used to run models of climate in the past. The results of running these models can then be used to make predictions about future climate changes. As well as running on supercomputers, the work of modelling climate change is also allocated to millions of personal computers around the world, via a technology known as distributed computing. The modelling task is broken down into millions of small tasks that are allocated to millions of processing units, which return the results of processing each task to the server and then receive further tasks.