yr−1. Magnetic tapes are used in offline system to store data and most of the analysis is accomplished here. The offline processing system is designed platform-independent because different computer architectures are used for data analysis. Because of this, the data structures are based on ZEBRA bank system developed in CERN as well as the ZEBRA exchange system. Event data from Super-Kamiokande online DAQ system basically contains a list of number of hit PMT, TDC and ADC counts, GPS time-stamps and other housekeeping data. For solar neutrino analysis, lowering the energy threshold is a constant goal, so it is a continual effort to improve the efficiency of reduction algorithms; however, changes in calibrations or reduction methods require reprocessing of earlier data. Typically, 10 Tbytes of raw data is processed every month so that a large amount of CPU power and high-speed I/O access to the raw data. In addition, extensive Monte Carlo simulation processing is also necessary. Offline system was designed to meet demand of all these: tape storage of a large database (14 Tbytes yr−1), stable semi-realtime processing, nearly continuous re-processing and Monte Carlo simulation. The computer system consists of 3 major sub-systems: the data server, the CPU farm and the network at the end of Run I. In US A system dedicated to offsite offline data processing was set up at the Stony Brook University in Stony Brook, NY to process raw data sent from Kamioka. Most of the reformatted raw data is copied from system facility in Kamioka. At Stony Brook, a system was set up for analysis and further processing. At Stony Brook the raw data were processed with a multi-tape DLT drive. The first stage data reduction processes were done for the high energy analysis and for the low energy analysis. The data reduction for the high energy analysis was mainly for atmospheric neutrino events and proton decay search while the low energy analysis was mainly for the solar neutrino events. The reduced data for the high energy analysis was further filtered by other reduction processes and the resulting data were stored on disks. The reduced data for the low energy were stored on DLT tapes and sent to University of California, Irvine for further processing. This offset analysis system continued for 3 years until their analysis chains were proved to produce equivalent results. Thus, in order to limit manpower, collaborations were concentrated to a single