Abstract
Article history: Received September 18, 2014 Accepted 15 December 2014 Available online December 16 2014 This paper concentrates on the evaluation of reliability measures of a computer system of twoidentical units having independent failure of h/w and s/w components. Initially one unit is operative and the other is kept as spare in cold standby. There is a single server visiting the system immediately whenever needed. The server conducts preventive maintenance of the unit after a maximum operation time. If server is unable to repair the h/w components in maximum repair time, then components in the unit are replaced immediately by new one. However, only replacement of the s/w components has been made at their failure. The priority is given to the preventive maintenance over repair activities of the h/w. The time to failure of the components follows negative exponential distribution whereas the distribution of preventive maintenance, repair and replacement time are taken as arbitrary. The expressions for some important reliability measures of system effectiveness have been derived using semi-Markov process and regenerative point technique. The graphical behavior of the results has also been shown for a particular case. Growing Science Ltd. All rights reserved. 5 © 201
Highlights
Over the past few decades, the demand of reliable h/w and s/w components has increased manifolds due to their applications in every sphere of life, in industrial management
G(t) e t, h(t) e t, f (t) e t and m(t) e t, the graphs for mean time to system failure (MTSF), availability and profit are drawn with respect to preventive maintenance rate (α) for fixed values of other parameters as shown respectively in Figs. 2 to 4
These figures indicate that MTSF, Availability and profit increase with the increase of PM rate (α) and repair rate (θ) of the hardware components
Summary
Over the past few decades, the demand of reliable h/w and s/w components has increased manifolds due to their applications in every sphere of life, in industrial management. Kumar et al (2012) and Malik and Kumar (2012) proposed a reliability model for computer system introducing the concept of preventive maintenance of the unit after a maximum operation time and repair time. The time to failure of the components follows negative exponential distribution whereas the distribution of preventive maintenance, repair and replacement time are taken as arbitrary. The expressions for some important reliability measures of system effectiveness such as mean time to system failure (MTSF), availability, busy period of the server due to PM, busy period of the server due to h/w repair, busy period of the server due to h/w replacement, busy period of the server due to s/w replacement, expected number of h/w replacements, expected number of s/w replacements, expected number of visits of the server and profit function are obtained using semi-Markov and regenerative point technique. The graphical behavior of MTSF, availability and profit function has been observed for a particular case
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