# Latency Numbers

Latency Comparison Numbers (\~2012)

Sourced from [Latency Numbers Every Programmer Should Know | GitHub](https://gist.github.com/jboner/2841832)

| Item                               | ns          | us      | ms  | more                        |
| ---------------------------------- | ----------- | ------- | --- | --------------------------- |
| L1 cache reference                 | 0.5         |         |     |                             |
| Branch mispredict                  | 5           |         |     |                             |
| L2 cache reference                 | 7           |         |     | 14x L1 cache                |
| Mutex lock/unlock                  | 25          |         |     |                             |
| Main memory reference              | 100         |         |     | 20x L2 cache, 200x L1 cache |
| Compress 1K bytes with Zippy       | 3,000       | 3       |     |                             |
| Send 1K bytes over 1 Gbps network  | 10,000      | 10      |     |                             |
| Read 4K randomly from SSD\*        | 150,000     | 150     |     | \~1GB/sec SSD               |
| Read 1 MB sequentially from memory | 250,000     | 250     |     |                             |
| Round trip within same datacenter  | 500,000     | 500     |     |                             |
| Read 1 MB sequentially from SSD\*  | 1,000,000   | 1,000   | 1   | \~1GB/sec SSD, 4X memory    |
| Disk seek                          | 10,000,000  | 10,000  | 10  | 20x datacenter roundtrip    |
| Read 1 MB sequentially from disk   | 20,000,000  | 20,000  | 20  | 80x memory, 20X SSD         |
| Send packet CA->Netherlands->CA    | 150,000,000 | 150,000 | 150 |                             |

note that,

* 1 ns = 10^-9 seconds
* 1 us = 10^-6 seconds = 1,000 ns
* 1 ms = 10^-3 seconds = 1,000 us = 1,000,000 ns

\--

## Credit

By Jeff Dean: <http://research.google.com/people/jeff/>\
Originally by Peter Norvig: <http://norvig.com/21-days.html#answers>

## Contributions

'Humanized' comparison: <https://gist.github.com/hellerbarde/2843375>\
Visual comparison chart: <http://i.imgur.com/k0t1e.png>