On the question of the reliability of computer systems with a quasi-structure

Abstract

Abstract. The paper discusses the use of a simple phenomenological model in order to determine the analytical dependence of the credibility functions of computer systems (CS), depending on the type of structures and their characteristics. Failures and outages in the operation of information management systems, as well as software flaws that were not detected during the design process, lead to errors that result in decreasing the credibility of calculations and, as a result, unpredictable behavior of the control system. For the first time, such a characteristic as “credibility” was included by A. Avizhenis (Algirdas Avizienis) in the list of basic attributes of the CS dependability. It is known that with increasing credibility of the functioning of CS, the credibility of the generated information or the control action on a controlled object (CO) increases as well, but for redundant CS the structures of which are characterized by the fault tolerance property do not have such direct relationship. Analysis of the structural reliability and credibility of the functioning of various redundant structures of the CS showed that the majority structures have a higher level of credibility of functioning compared to other redundant structures that exceed their reliability. However, recently, among the well-known redundant CS structures used for ensuring fault tolerance, a new two-channel self-verifiable quasi-bridge structure (QBS) has appeared, the credibility of which has not been previously investigated. The paper shows that the QBS, having in its composition modules with a higher individual reliability, compared with the modules included in the other analyzed structures, is characterized by a low two-fold hardware redundancy, while winning at the same time with majority structures with three and five-fold hardware redundancy, as on the evaluation of the basic model of reliability (probability of failure-free operation), and on the credibility of operation. Keywords: credibility, probability of failure-free operation, quasi-bridge structure, credibility of functioning calculation.