In this paper, the reliability characteristics of a parallel system are investigated. The parallel system under consideration is made up of three active units that run in parallel, with two of them having to be operational in order for the system to work. The main purpose of this study is to quantify/examine the effect of online and offline preventive maintenance. Preventive maintenance is carried out on the systems in two ways: online and offline preventive mainte-nance. After the first unit of each system fails, online preventive maintenance is performed. Following the failure of the second unit of each system, offline preventive maintenance is performed. Partial and complete failures are the two types of failures that may occur. Both systems can undergo exponential failure and repair. Using supplementary variable technique, Laplace transform, and Copula repair approach, the system of first-order differential equa-tions associated with system effectiveness, which are crucial to this research, is established and resolved. Tables and graphs are used to illustrate the important findings based on assumed numerical values. System designers, programmers, and maintenance supervisors will be able to create and maintain more crucial systems with the assistance of this research paper.