### Latency numbers every programmer should know
    L1 cache reference ......................... 0.5 ns
    Branch mispredict ............................ 5 ns                     on recent CPU
    L2 cache reference ........................... 7 ns                     14x L1 cache
    Mutex lock/unlock ........................... 25 ns
    Main memory reference ...................... 100 ns                     20x L2 cache, 200x L1 cache
    Compress 1K bytes with Zippy ............. 3,000 ns  =   3 µs
    Send 2K bytes over 1 Gbps network ....... 20,000 ns  =  20 µs
    SSD random read ........................ 150,000 ns  = 150 µs
    Read 1 MB sequentially from memory ..... 250,000 ns  = 250 µs           4X memory
    Round trip within same datacenter ...... 500,000 ns  = 0.5 ms           20x datacenter roundtrip
    Read 1 MB sequentially from SSD* ..... 1,000,000 ns  =   1 ms           80x memory, 20X SSD
    Disk seek ........................... 10,000,000 ns  =  10 ms
    Read 1 MB sequentially from disk .... 20,000,000 ns  =  20 ms
    Send packet CA->Netherlands->CA .... 150,000,000 ns  = 150 ms
    LTO4 tape seek/access time ...... 55.000.000.000 ns  =  55 s

Assuming ~1GB/sec SSD

![Visual representation of latencies](http://i.imgur.com/k0t1e.png)

Evolution over Years [Berkeley](http://www.eecs.berkeley.edu/~rcs/research/interactive_latency.html)

Pings around the world [WonderNetwork](https://wondernetwork.com/pings)

PC Hardware Speeds [Gustavo Duartes](http://duartes.org/gustavo/blog/post/what-your-computer-does-while-you-wait)


Visual chart provided by [ayshen](https://gist.github.com/ayshen)

Data by [Jeff Dean](http://research.google.com/people/jeff/)

Originally by [Peter Norvig](http://norvig.com/21-days.html#answers)