System Design (50 Qs)•Part 5: Back-of-the-Envelope Estimation & Production Calculations (44 - 50)
Latency Numbers Every Software Engineer Should Know.
In Simple Words: Approximate physical hardware latencies that dictate architectural trade-offs:
| Operation | Approximate Latency | Scaled to Human Perspective |
|---|---|---|
| L1 Cache Reference | 0.5 ns | 1 heart beat |
| L2 Cache Reference | 7 ns | 14 heart beats |
| RAM Main Memory Reference | 100 ns | 3.3 minutes |
| NVMe SSD Random Read | 10,000 ns (10 µs) | 5.5 hours |
| Standard Datacenter Network RTT | 500,000 ns (0.5 ms) | 11.5 days |
| Disk Seek (Mechanical HDD) | 10,000,000 ns (10 ms) | 8 months |
| Transatlantic Cable Packet (NYC to London) | 100,000,000 ns (100 ms) | 6.5 years |