Fermi Estimation Case: Counting the Computers at LinkedIn

An interviewer asks you to estimate the number of computers that LinkedIn, the professional networking company, has. Lay out your structure, state every input as a labeled assumption with round numbers, do the arithmetic, and sanity-check the result. ```hint Different drivers Not every kind of computer grows with the same thing. Ask what each kind scales with, estimate each population on its own, and only then add them up. ``` ### Clarifying Questions - What counts as a computer: only the laptops and desktops people work on, or also the servers that run the website and apps? - Should machines used by contractors, shared machines in meeting rooms and spare inventory be included? - Do machines LinkedIn rents from a cloud provider count, or only machines it owns and operates? ### What a Strong Answer Covers - An agreed definition of what counts before any numbers appear - An equation that splits the total into populations with different drivers - Each input stated as a labeled, round-number assumption, with arithmetic that checks out - A sanity check from an independent angle - A range, plus the assumptions the answer is most sensitive to ### Follow-up Questions - Which single assumption moves your answer the most, and how would you narrow it down? - How would your number change if most of LinkedIn's workloads ran in a public cloud? - About how many of these computers would need to be replaced each year?