The present correlator handles one side band of 16 MHz bandwidth. The MAC unit consists of three racks, and the data is hence received over three channels. The host computer uses a custom made card to accept data at three separate ports. In order to maintain standard time for reference for the data blocks, the host computer is also provided with minute pulses from the Global Positioning System (GPS). One of the fundamental cycles of the correlator operation is the Short Term Accumulation (STA) cycle, over which the MAC unit accumulates the data; it is equivalent to 8192 cycles of FFT. The clock edges that signify the beginning of STA cycles are also provided to the computer. The STA cycle timings are used to maintain the synchronization in the communication between the host computer and the correlator components. This STA clock edge also signifies the beginning of the STA data cycle. The actual communication for the control of the correlator components takes place via another custom made, in-house developed card which can communicate to sixteen different components sequentially.
So far, the connections were described on the correlator side of the interface (host) computer. The major data processing and correlator control is carried out by the same host computer. On the other side of the interface computer is the `network' i.e. a connection via the standard Internet Protocol over Ethernet. One of the computers on this network side is used by the observers to control and monitor the entire GMRT system. Commands are issued by this computer (`Observers Command Desk' in Figure 26.2) to the host computer which in turn manages the correlator. Another network component, the `Data Recording Host' (figure 26.2) is used for data storage and off-line processing. This computer is the main compute server and has a huge data storage capability.