11.1 Introduction

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This chapter will assume that a system or component is functional, or not. In practice systems fail slowly, but we will consider failure to be when they cease being functional.

No system is perfect and will fail eventually, being able to predict this allows us to determine the useable life.

Dependability is a combination of,

- reliability - the probability that a system operates through a given operation specification.

- availability - the probability that the system will be available at any instant required.

Typical failures follow the following curve.