Latency Comparison Numbers (~2012)
----------------------------------
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
Local LLM, generate 1 token         15,000,000   ns   15,000 us   15 ms  Small model on consumer GPU (2026)
Read 1 MB sequentially from disk    20,000,000   ns   20,000 us   20 ms  80x memory, 20X SSD
Frontier LLM, generate 1 token      20,000,000   ns   20,000 us   20 ms  Hosted model output (2026)
Local LLM, time to first token      75,000,000   ns   75,000 us   75 ms  Small model, short prompt (2026)
Local LLM (CPU), generate 1 token  100,000,000   ns  100,000 us  100 ms  Small model, no GPU (2026)
Send packet CA->Netherlands->CA    150,000,000   ns  150,000 us  150 ms
Fast LLM, time to first token      250,000,000   ns  250,000 us  250 ms  Specialized inference hardware (2026)
Frontier LLM, time to first token                              1,000 ms  Short prompt, no cache (2026)
Frontier LLM, short response                                   3,000 ms  ~100 output tokens (2026)
Frontier LLM, long context prefill                            10,000 ms  ~100K input tokens, no cache (2026)
Frontier LLM, reasoning response                              30,000 ms  Single call with thinking (2026)

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
-------------
'Humanized' comparison:    https://gist.github.com/hellerbarde/2843375
Visual comparison chart:   http://i.imgur.com/k0t1e.png
Interactive Prezi version: https://prezi.com/pdkvgys-r0y6/latency-numbers-for-programmers-web-development/latency.txt