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.
Dell laptops are not supposed to be that strong and their life varies from model to model. The XPS and alienware have a better life while the inspiron have a moderate life. The Vostro Edition doesn't have that much life. The average life for the Dell laptop hardware is almost 3-4 years if handled with care. Also, they get pretty much out of date in 2 or 3 years so you have to change it.