This paper addresses an observer-design method only using data. Usually, the observer requires a mathematical model of a system for state prediction and observer gain calculation. As an alternative to the model-based prediction, the proposed predictor calculates the states using a linear combination of the given data. To design the observer gain, the data which represent dual systems are derived from the data which represent the original system. Linear matrix inequalities that depend on data of the dual system provides the observer gains.

The fault tolerant computer (FTC) is applied as a communication or database server in the information service and computer aided process control fields. User requires of the FTC are to provide the current level of performance and software transparency needing no additional dedicated program for fault tolerance. To meet these requirements, we propose quadprocessor redundancy (QPR) architecture that combines dualRISC based duplicated CPUs integrating main memories, and duplicated I/O subsystems by using some additional hardware. Duplicated CPUs run under the instruction level synchronization (lock step operation) , and the duplicated I/O subsystems are managed by an operating system. When a fault is detected, the faulty CPU is isolated by hardware. User program is continuously executed by the remaining CPU. We applied the QPR to our UNIX servers, and achieved satisfactory levels of performance.