The data acquisition and reduction challenge at the Large Hadron Collider

The Large Hadron Collider detectors are technological marvels—which resemble, in functionality, three-dimensional digital cameras with 100 Mpixels—capable of observing proton–proton (pp) collisions at the crossing rate of 40 MHz. Data handling limitations at the recording end imply the selection of only one pp event out of each 105. The readout and processing of this huge amount of information, along with the selection of the best approximately 200 events every second, is carried out by a trigger and data acquisition system, supplemented by a sophisticated control and monitor system. This paper presents an overview of the challenges that the development of these systems has presented over the past 15 years. It concludes with a short historical perspective, some lessons learnt and a few thoughts on the future.