The brain of the cold universe
At 5,000 meters (16,500 feet) on the Chajnantor Plateau, inside the highest-altitude high-tech building in the world, is one of the fastest special-purpose supercomputers ever built. The ALMA Correlator is the digital brain of the Atacama Large Millimeter/submillimeter Array (ALMA), a collection of 66 precision radio antennas observing the "cold universe," the faint radio waves emitted by cosmic dust, gas clouds, and some of the earliest galaxies. Its sole task is to combine the immense volume of data collected by the antennas, which are spread out over distances of up to 16 kilometers.
This process, called interferometry, allows the 66 separate dishes to function as a single, gigantic telescope. The correlator must cross-correlate the signals from every possible pair of antennas. With up to 64 antennas operating at once, this means it handles 2,016 unique pairings. To accomplish this, the machine's 134 million processors perform up to 17 quadrillion (17,000,000,000,000,000) mathematical operations every second. This computational speed is comparable to the fastest general-purpose supercomputers in the world. The raw data rate from the antennas can reach 750 gigabytes per second, a volume too large to store, making real-time processing necessary.
Computing at extreme altitude
Operating such a powerful computer in this location presents enormous engineering challenges. The machine draws about 140 kilowatts of power, generating substantial heat. At 5,000 meters, the air density is roughly half that at sea level, which makes conventional air cooling inefficient. To compensate, twice the normal airflow is required to prevent the electronics from overheating.
The thin air also forbids the use of standard spinning hard disk drives. The read/write heads in these drives float on a cushion of air that is too thin at this altitude, so the correlator must be entirely diskless. Data is processed instantly and then transmitted down to the ALMA Operations Support Facility (OSF), located at a more manageable altitude of 2,900 meters (9,500 feet), for storage and analysis. The entire structure is also designed to withstand frequent seismic activity common in the Andes.