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.
Ed Roberts, creator of early PC, dies. Roberts, whose MITS Altair 8800 is often cited as the original personal computer, died Thursday at age 68. Ed Roberts, whose early Altair 8800 computer helped inspire Bill Gates and Paul Allen to start Microsoft, died Thursday. He was 68.