  The new era of software signal processing has a large impact on radio
astronomy instrumentation. Our design and implementation of a 32 antennae, 33
MHz, dual polarization, fully real-time software backend for the GMRT, using
only off-the-shelf components, is an example of this. We have built a
correlator and a beamformer, using PCI-based ADC cards and a Linux cluster of
48 nodes with dual gigabit inter-node connectivity for real-time data transfer
requirements. The highly optimized compute pipeline uses cache efficient,
multi-threaded parallel code, with the aid of vectorized processing. This
backend allows flexibility in final time and frequency resolutions, and the
ability to implement algorithms for radio frequency interference rejection. Our
approach has allowed relatively rapid development of a fairly sophisticated and
flexible backend receiver system for the GMRT, which will greatly enhance the
productivity of the telescope. In this paper we describe some of the first
lights using this software processing pipeline. We believe this is the first
instance of such a real-time observatory backend for an intermediate sized
array like the GMRT.
