Since the initial startup of Hanford's 800 MW(e) N Reactor, a number of digital computer applications have been implemented to assist in the maintenance and operation of the reactor complex. Two information systems were developed: one for storing reactor operating data and fuel-element charge-discharge information, and the other for keeping detailed records on equipment maintenance and associated costs. Both off-line and on-line computer codes have been written for calculating reactor operating limits and reactor parameters not measured directly. This use of an on-line computer for the calculation of process control parameters in conjunction with a large general-purpose computer to maintain reactor information systems has been demonstrated as an effective means of administering reactor process limits and reducing vast amounts of operational and inventory data into acceptable formats.