High-performance computing (HPC) used to be all about buying the fastest system you could afford. It was simple: You had a problem, and you spent as much money as you could to buy a single fast system. Then, some clever people (Thomas Sterling and Donald Becker at NASA) came along and pointed out that computers had gotten quite a bit faster, and if they worked together, they could solve certain types of problems just as quickly for much less money. So, these folks took some commodity hardware and Ethernet gear, wrote some software to tie it all together, and created the Beowulf cluster [1].

Since then, the TOP500 supercomputer list [2] has changed from a list of systems running specialized software from Cray and friends – with a handful of distributed systems running Linux at the bottom – to a list of almost completely Linux-based systems (95.2% of systems and 97.4% of performance as of June 2013), while silicon speeds have basically topped out at 5GHz. Sure, you can go faster, but it's more expensive; going horizontal is much more cost effective.

All of these developments have made HPC vastly more affordable. The technologies and software designed and built to allow commodity hardware to handle large loads also work very well at a smaller scale. This means you can build a solution at a small scale (e.g., using Hadoop, memcached, MongoDB, CouchDB, MapReduce, etc.) and simply add nodes to scale up as necessary. You don't need to replace the system or make significant changes to the software, you can just add more systems running the exact same software.

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