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Numbers Everyone Should Know

  • https://everythingisdata.wordpress.com/2009/10/17/numbers-everyone-should-know/

  • Operation Time (nsec)

  • L1 cache reference 0.5

  • Branch mispredict 5

  • L2 cache reference 7

  • Mutex lock/unlock 25

  • Main memory reference 100

  • Compress 1KB bytes with Zippy 3,000

  • Send 2K bytes over 1 Gbps network 20,000

  • Read 1MB sequentially from memory 250,000

  • Roundtrip within same datacenter 500,000

  • Disk seek 10,000,000

  • Read 1MB sequentially from disk 20,000,000

  • Send packet CA -> Netherlands -> CA 150,000,000

  • Operation Time (nsec)

  • System call overhead 400

  • Context switch between processes 3000

  • fork() (statically-linked binary) 70,000

  • fork() (dynamically-linked binary) 160,000

Memory Speed Hierarchy

  • CPU processor:
    • Register (fastest)
    • Cache (Cache > L1 > L2)
  • Main memory (varied over time, large RAM chips read faster than ROM):
    • RAM
    • ROM, BIOS
  • Solid state drive:
    • Magnetic disks
  • Magnetic tapes