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Here's the output of top:

top - 23:30:49 up  2:18,  1 user,  load average: 4.36, 4.36, 4.39
Tasks: 105 total,   2 running, 103 sleeping,   0 stopped,   0 zombie
Cpu(s):  3.6%us,  8.0%sy,  0.0%ni, 73.4%id,  9.0%wa,  1.1%hi,  4.9%si,  0.0%st
Mem:   2029820k total,  1979312k used,    50508k free,     6828k buffers
Swap:  5947384k total,        0k used,  5947384k free,  1855304k cached

How can the load average be high while the CPU load is low.

How is load average calculated?

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What are you running, it seems your system is working on something. I get loads like that when I compress a bunch of stuff while compiling. –  NightwishFan Oct 25 '10 at 22:15
    
I always thought of the load as the "number of processes waiting to be executed", but I'm not really sure if that is correct. –  pableu Oct 26 '10 at 7:21
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2 Answers

What Inigoesdr and the site he/she points to write is more or less correct, but remember that the "load average" isn't really a "regular" mathematical average, it's a exponentially damped/weighted moving average.

This is a very good and in-depth article on the topic of CPU percentage and load average, and how they are calculated in linux. Wikipedia also has a good article on it (explaining some differences between load average on linux vs. most UNIX systems for example).

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This site does a good job of explaining it. Basically, load average is the amount of traffic to your CPU(s) over the past 1, 5, and 15 minutes. Generally you want this number to be below the number of CPU(s)/cores you have. 1.0 on a single core machine means it's using the CPU to it's maximum, and anything above that means things are getting queued.

The CPU line in your top output is the current usage broken down by process types.

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As a note, load average also includes processes waiting on I/O: serverfault.com/a/524818/27813 –  rogerdpack Jul 19 '13 at 17:49
    
The linked site has a really good explanation. –  AsheeshR Sep 22 '13 at 10:53
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