Back-of-the-Envelope Estimation

**Key numbers every engineer should know:** **Latency:** - L1 cache: 0.5 ns - L2 cache: 7 ns - RAM: 100 ns - SSD random read: 150 μs - HDD seek: 10 ms - Network round trip (same datacenter): 500 μs - Network round trip (cross-continent): 150 ms **Throughput:** - SSD: 1 GB/s - Network (1 Gbps): 125 MB/s - HDD: 100 MB/s **Storage:** - 1 char = 1 byte (ASCII) or 2 bytes (Unicode) - 1 million rows × 1KB = 1 GB - 1 billion rows × 1KB = 1 TB **Scale:** - 1M requests/day = ~12 requests/sec - 1B requests/day = ~12,000 requests/sec - 86,400 seconds in a day (round to 100K for estimates) **Power of 2:** - 2^10 ≈ 1 thousand (1 KB) - 2^20 ≈ 1 million (1 MB) - 2^30 ≈ 1 billion (1 GB) - 2^40 ≈ 1 trillion (1 TB)