There were four basic materials that the Egyptians used to build the pyramids: limestone, pink granite, basalt, and alabaster. Each type of material had a diverse use. Limestone had, for the most part, two uses.
To answer your question: The useful lifespan of a CPU is about 3-4 years. My guess on the technical lifespan under full load is closer to 8-10 years if nothing else breaks and takes the CPU with it. The reasons: High Performance Computing Clusters usually keep the computers for 3-4 years.
Mathematically, life expectancy is the mean number of years of life remaining at a given age, assuming constant mortality rates. It is denoted by, which means the average number of subsequent years of life for someone now aged, according to a particular mortality experience.he term life expectancy may also be used in the context of manufactured objects, although the related term shelf life is used for consumer products and the terms mean time to breakdown (MTTB) and  mean time between failures  (MTBF) are used in engineering.