The Large Hadron Collider's worldwide computer

Behind the excellent results from CERN's Large Hadron Collider (LHC) lies the Worldwide LHC Computing Grid – a giant that never sleeps. Find out more in this recent feature article from the CERN Courier...

Mid-February marked the end of the first three-year run of CERN's Large Hadron collider (LHC). While the machine exceeded all expectations, delivering significantly more data to the experiments than initially foreseen, high-performance distributed computing also enabled physicists to announce on 4 July the discovery of a new particle. With the first run now over, it is a good time to look back at the Worldwide LHC Computing Grid to see what was initially planned, how it performed and what is foreseen for the future.

Back in the late 1990s, it was already clear that the expected amount of LHC data would far exceed the computing capacity at CERN alone. Distributed computing was the sensible choice. The first model proposed was MONARC (Models of Networked Analysis at Regional Centres for LHC Experiments), on which the experiments originally based their computing models. In September 2001, CERN Council approved the first phase of the LHC Computing Grid project, led by Les Robertson of CERN’s IT department. From 2002 to 2005, staff at CERN and collaborating institutes around the world developed prototype equipment and techniques. From 2006, the LHC Computing Grid became the Worldwide LHC Computing Grid (WLCG) as global computing centres became connected to CERN to help store data and provide computing power.

A wealth of data

WLCG uses a tier structure with the CERN data centre as Tier 0. CERN sends out data to each of the 11 major data centres around the world that form the first level, or Tier 1, via optical-fibre links working at multiples of 10 Gbit/s. Each Tier 1 site is then linked to a number of Tier 2 sites, usually located in the same geographical region. Computing resources are supported by the national funding agencies of the countries where each tier is located.

Read more: "The Large Hadron Collider's worldwide computer" - reproduced on International Science Grid This Week