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Google·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say
May 2026

Summary

Got a fermi estimation question at Google that sounds deceptively simple but spirals fast once you start actually thinking about it.

Questions Asked (1)

Q1

Estimate how much storage would be required to hold all the information your brain processes in a single day.

System DesignTechnical Trade-offsAdaptability & Ambiguity
Author's notes

I stared at this for a second because I had no idea where to anchor.

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AI HintsAI Generated

Suggested Approach

Break the problem into sensory input channels (visual, auditory, tactile, etc.) and estimate the raw data rate for each, then sum and convert to bytes. Clearly state assumptions about compression, attention filtering, and what 'process' means (raw sensory data vs. conscious thoughts).

Pro tip: Acknowledge that the brain compresses and filters heavily, so the raw sensory estimate is an upper bound; mention that conscious processing is orders of magnitude smaller, showing you understand the distinction between data and information.

1. Clarify scope and assumptions

Define what 'process' means: raw sensory input, neural activity, or conscious thoughts. State that you'll estimate raw sensory data as an upper bound, assuming continuous waking hours (e.g., 16 hours).

2. Estimate per-channel data rates

For each major sense, estimate bandwidth: vision (e.g., 10 Mbps based on optic nerve), hearing (e.g., 1 Mbps), touch, smell, etc. Use known physiological limits or reasonable guesses.

3. Sum and convert to daily storage

Add the channel rates to get total bits per second, multiply by seconds per day (e.g., 16 hours * 3600 s), and convert to bytes (divide by 8).

4. Apply compression and filtering factors

Discuss how the brain compresses data (e.g., predictive coding) and filters unattended information. Provide a range: raw vs. compressed estimates.

5. Sanity-check and conclude

Compare your estimate to known storage scales (e.g., GB vs. TB) and acknowledge uncertainty. Summarize the final range and key assumptions.

Key Points to Mention

  • Sensory bandwidth estimates (e.g., vision ~10 Mbps, hearing ~1 Mbps)
  • Duration of waking hours (e.g., 16 hours) and conversion to seconds
  • Difference between raw sensory data and conscious processing
  • Brain's compression and predictive coding mechanisms
  • Units: bits vs. bytes, and scaling to GB/TB
  • Acknowledgment of assumptions and uncertainty in estimates

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.