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Component Failures, Infant Mortality, and the Bathtub Curve

PC components, and in fact many electronic devices in general, tend to fail in a particular way. Understanding how this works is important in helping you decide how you want to deal with problems and component failures within your PC. The standard impression that many people who are less familiar with computers have, is that failures of components are roughly linear. A certain percentage of all components fail, and this failure rate is consistent within the life of the product, although it increases as the product gets older. This is in fact not the case. The failure rate of most components is remarkably non-linear.

PC component failures actually fall into three main periods, chronologically:

• Infancy: Many components fail very soon after they are put into service. How long this takes depends on the component; for example, processors sometimes fail as soon as they are first put into a system. Many other parts fail within a week or a month of being put into use. Failures within this period are caused by defects and poor design that cause an item to be legitimately bad. These are called infant mortality failures and the failure rate in this period is relatively high. Good system vendors will perform an operation called "burn in" where they put together and test a system for several days to try to weed out these types of problems so the customer doesn't see them.
• Normal Operating Life: If a component does not fail within its infancy, it will generally tend to remain trouble-free over its operating lifetime. Typical operating lifetimes for various components are shown in this section. The failure rate during this period is typically quite low.
• Wearout: After a component reaches a certain age, it enters the period where it begins to wear out, and failures start to increase. When this occurs of course is a matter of luck and also how well you take care of your PC. For example, processors tend to last years longer if they are operated in a cool environment as opposed to a warm one. The period where failures start to increase is called the wearout phase of component life.

If you examine a graph of failure rate versus time elapsed since a product was installed, you will see a large number of failures early on, then very few, with the number starting to increase as the wearout period is entered. This is often called a bathtub curve due to the approximate shape it makes (but note that the right-hand part of the curve usually has a much more gradual slope, because wearout takes time).

Next: System and Component Life

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