The High Energy Stereoscopic System (H.E.S.S.) is a system of Imaging
Atmospheric Cherenkov Telescopes (IACTs) located in the Khomas Highland in
Namibia. It measures cosmic gamma rays of very high energies (VHE; >100 GeV)
using the Earth's atmosphere as a calorimeter. The H.E.S.S. Array entered Phase
II in September 2012 with the inauguration of a fifth telescope that is larger
and more complex than the other four. This paper will give an overview of the
current H.E.S.S. central data acquisition (DAQ) system with particular emphasis
on the upgrades made to integrate the fifth telescope into the array. At first,
the various requirements for the central DAQ are discussed then the general
design principles employed to fulfil these requirements are described. Finally,
the performance, stability and reliability of the H.E.S.S. central DAQ are
presented. One of the major accomplishments is that less than 0.8% of
observation time has been lost due to central DAQ problems since 2009.Comment: 17 pages, 8 figures, published in Astroparticle Physic