Latency Numbers Every Programmer Should Know

latency.txt

Latency Comparison Numbers
--------------------------
L1 cache reference                           0.5 ns
Branch mispredict                            5   ns
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 us
Send 1K bytes over 1 Gbps network       10,000   ns       10 us
Read 4K randomly from SSD*             150,000   ns      150 us          ~1GB/sec SSD
Read 1 MB sequentially from memory     250,000   ns      250 us
Round trip within same datacenter      500,000   ns      500 us
Read 1 MB sequentially from SSD*     1,000,000   ns    1,000 us    1 ms  ~1GB/sec SSD, 4X memory
Disk seek                           10,000,000   ns   10,000 us   10 ms  20x datacenter roundtrip
Read 1 MB sequentially from disk    20,000,000   ns   20,000 us   20 ms  80x memory, 20X SSD
Send packet CA->Netherlands->CA    150,000,000   ns  150,000 us  150 ms

Notes
-----
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
-------------
Some updates from:       https://gist.github.com/2843375
'Humanized' comparison:  https://gist.github.com/2843375
Visual comparison chart: http://i.imgur.com/k0t1e.png
Animated presentation:   http://prezi.com/pdkvgys-r0y6/latency-numbers-for-programmers-web-development/latency.txt

Same table, but with nanoseconds scaled up to  seconds.

Latency Comparison Numbers - If they happened in "human" time (ns scaled up to seconds)
--------------------------
L1 cache reference                           1/2              0.5s  			(One to five times the blink of an eye)
Branch mispredict                            5                  5s
L2 cache reference                           7                  7s 
Mutex lock/unlock                           25                 25s
Main memory reference                      100              1m 40s
Compress 1K bytes with Zippy             3,000             50m 00s       (Length of a standard college lecture)
Send 1K bytes over 1 Gbps network       10,000          2h 45m 40s        
Read 4K randomly from SSD*             150,000      1d 17h 40m 00s
Read 1 MB sequentially from memory     250,000      2d 21h 26m 40s       (About  9 work days (8 hour days))
Round trip within same datacenter      500,000      5d 18h 53m 20s       (About 17 work days (8 hour days))
Read 1 MB sequentially from SSD*     1,000,000     11d 13h 46m 40s   
Disk seek                           10,000,000    115d 17h 46m 40s
Read 1 MB sequentially from disk    20,000,000    231d 11h 33m 20s
Send packet CA->Netherlands->CA    150,000,000 4y 280d  3h  0m  0s

Credit - (for normal version)
------
By Jeff Dean:               http://research.google.com/people/jeff/
Originally by Peter Norvig: http://norvig.com/21-days.html#answers

Contributions
-------------
Some updates from:       https://gist.github.com/2843375
'Humanized' comparison:  https://gist.github.com/2843375
Visual comparison chart: http://i.imgur.com/k0t1e.png
Animated presentation:   http://prezi.com/pdkvgys-r0y6/latency-numbers-for-programmers-web-development/latency.txt