latency_numbers.md

Latency numbers (cheat sheet)

Operation	nanosec	microsec	millisec	notable	1Bx
L1 cache reference	0.5 ns				0.5 s
Branch mispredict	5 ns				5 s
L2 cache reference	7 ns			14x L1 cache	7 s
Mutex lock/unlock	25 ns				25 s
Main memory reference	100 ns			20x L2 cache, 200x L1 cache	1.6 m
Compress 1K bytes with Zippy	3,000 ns	3 µs			50 m
Send 1K bytes over 1Gbps net	10,000 ns	10 µs			5.5 h
Read 4K randomly from SSD	150,000 ns	150 µs		~1GB/s SSD	1.7 d
Read 1MB sequentially from mem	250,000 ns	250 µs		~4GB/s mem	2.9 d
Round trip within same datacenter	500,000 ns	500 µs			5.8 d
Read 1MB sequentially from SSD	1,000,000 ns	1,000 µs	1 ms	~1GB/s SSD (4x mem)	11.6 d
Disk seek	10,000,000 ns	10,000 µs	10 ms	20x datacenter roundtrip	16.5 w
Read 1MB sequentially from Disk	20,000,000 ns	20,000 µs	20 ms	50MB/s (80x mem / 20s SSD)	7.6 m
Send pack et CA->Netherlands->CA	150,000,000 ns	150,000 µs	150 ms		4.75 y

Note: the 1Bx column represents the values multiplied by 1 billion, to help mentally visualize the scale and proportions.

Notes

1 ns (nanosecond)  = 10^-9 s

1 µs (microsecond) = 10^-6 s  =     1,000 ns

1 ms (millisecond) = 10^-3 s  =     1,000 µs =     1,000,000 ns

1 s  (second)      = 1,000 ms = 1,000,000 µs = 1,000,000,000 ns

Credit

By Jeff Dean: http://research.google.com/people/jeff/

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