ABSTRACT
Due to the ubiquitous provision of services on the internet, dependability has become an attribute of prime concern in hardware/software development, deployment, and operation. Providing fault-tolerant services is related inherently to the adoption of redundancy. Redundancy can be exploited either in time or in space. Replication of services usually is provided through distributed hosts across the world so that whenever the service, the underlying host, or network fails another service is ready to take over. The chapter focuses on background concepts on Markov chains and Stochastic Petri Nets (SPNs). It presents some availability and reliability models for computer systems. The chapter provides a summary of early work related to dependability and briefly describes some seminal efforts as well as the respective relations with current prevalent methods. It explains a very brief introduction to Continuous Time Markov Chains and SPNs, which are the formalism adopted to model availability and reliability.
