# Numbers every programmer should know

**[Numbers every programmer should know](https://colin-scott.github.io/personal_website/research/interactive_latency.html)** is a reference of hardware latencies: L1 cache (1ns), memory (100ns), SSD (1ms), network (10ms). These span orders of magnitude and shape every performance decision in systems design.

Based on Jeff Dean's seminal analysis; values evolve as technology changes.

## Example

Typical latency hierarchy (approximate 2020s values):

```
L1 cache reference:           1 ns
L2 cache reference:           7 ns
Main memory reference:       100 ns
Mutex lock/unlock:           100 ns
Compress 1K with Zippy:     3,000 ns
Network SSD read (4K):    150,000 ns
Disk seek:             10,000,000 ns
Network RTT CA↔NL:    150,000,000 ns
```