  The Murchison Widefield Array (MWA) is a Square Kilometre Array (SKA)
Precursor. The telescope is located at the Murchison Radio--astronomy
Observatory (MRO) in Western Australia (WA). The MWA consists of 4096 dipoles
arranged into 128 dual polarisation aperture arrays forming a connected element
interferometer that cross-correlates signals from all 256 inputs. A hybrid
approach to the correlation task is employed, with some processing stages being
performed by bespoke hardware, based on Field Programmable Gate Arrays (FPGAs),
and others by Graphics Processing Units (GPUs) housed in general purpose rack
mounted servers. The correlation capability required is approximately 8 TFLOPS
(Tera FLoating point Operations Per Second). The MWA has commenced operations
and the correlator is generating 8.3 TB/day of correlation products, that are
subsequently transferred 700 km from the MRO to Perth (WA) in real-time for
storage and offline processing. In this paper we outline the correlator design,
signal path, and processing elements and present the data format for the
internal and external interfaces.
