Numbers Everyone Should Know

Some of you have seen me build simple models to do a reality-check on architecture (see here, for example). Here are some metrics from a great presentation by Jeff Dean, a Google fellow.

Numbers Everyone Should Know

L1 cache reference 0.5 ns
Branch mispredict 5 ns
L2 cache reference 7 ns
Mutex lock/unlock 25 ns
Main memory reference 100 ns
Compress 1K bytes with Zippy 3,000 ns
Send 2K bytes over 1 Gbps network 20,000 ns
Read 1 MB sequentially from memory 250,000 ns
Round trip within same datacenter 500,000 ns
Disk seek 10,000,000 ns
Read 1 MB sequentially from disk 20,000,000 ns
Send packet CA->Netherlands->CA 150,000,000 ns

Of note is the 120X difference between the cost of reading 1MB from memory and the cost of reading 1MB from disk…

The entire presentation may be found here:

Happy Modeling…

One thought on “Numbers Everyone Should Know”

  1. It is worth noting that these numbers are circa 2009. Memory clock speeds improve based on Moore’s Law. Disk data transfer rates to not… so the 80X advantage of memory over disk listed here is conservative.

    These metrics provide the price/performance rationale for in-memory databases (IMDB).

    More on memory speeds can be found at:

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