A simplified block diagram of the GMRT correlator is shown in Fig. 25.2. The basic units are the analog to digital converters (ADC), the Integral Delay compensation (Delay-DPC) subsystem, the Fourier transform and fractional delay compensation (FFT) subsystem and the multiplier-accumulator (MAC) unit. The data from the MAC output is acquired using a special purpose PC add on card. All of the subsystems, except the ADC, have DSP (digital signal processor) based control circuits. These control circuits are in turn controlled by the data acquisition computer, (i.e. the same machine which acquires the data via the add on card; see Chapter 26 for more details).