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11.1 Introduction

• 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.