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An idle computer has a load number of 0 (the idle process isn't counted). Each [[process (computing)|process]] using or waiting for [[Central processing unit|CPU]] (the ''ready queue'' or [[run queue]]) increments the load number by 1. Each process that terminates decrements it by 1. Most UNIX systems count only processes in the ''running'' (on CPU) or ''runnable'' (waiting for CPU) [[Process states|states]]. However, Linux also includes processes in [[uninterruptible sleep]] states (usually waiting for [[Hard disk|disk]] activity), which can lead to markedly different results if many processes remain blocked in [[Input/output|I/O]] due to a busy or stalled I/O system.<ref>http://linuxtechsupport.blogspot.com/2008/10/what-exactly-is-load-average.html</ref> This, for example, includes processes blocking due to an [[Network File System (protocol)|NFS]] server failure or too slow [[Data storage device|media]] (e.g., [[Universal Serial Bus|USB]] 1.x storage devices). Such circumstances can result in an elevated load average which does not reflect an actual increase in CPU use (but still gives an idea of how long users have to wait).
Systems calculate the load ''average'' as the [[Moving average#Exponential moving average|exponentially damped/weighted moving average]] of the load ''number''. The three values of load average refer to the past one, five, and fifteen minutes of system operation.<ref name="drdobbs">{{cite web |url=http://www.linuxjournal.com/article/9001 |title=Examining Load Average |first=Ray |last=Walker |date=1 December 2006 |work=Linux Journal |
Mathematically speaking, all three values always average all the system load since the system started up. They all decay exponentially, but they decay at different ''speeds'': they decay exponentially by ''e'' after 1, 5, and 15 minutes respectively. Hence, the 1-minute load average consists of 63% (more precisely: 1 - 1/''e'') of the load from the last minute and 37% (1/''e'') of the average load since start up, excluding the last minute. For the 5- and 15-minute load averages, the same 63%/37% ratio is computed over 5 minutes and 15 minutes respectively. Therefore, it is not technically accurate that the 1-minute load average only includes the last 60 seconds of activity, as it includes 37% of the activity from the past, but it is correct to state that it includes ''mostly'' the last minute.
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|url = http://www.brendangregg.com/blog/2017-08-08/linux-load-averages.html
|date = 8 August 2017
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|author = [[Neil J. Gunther]]
|publisher = TeamQuest
|access-date =
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|author = Andre Lewis
|date = 31 July 2009
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}} Explanation using an illustrated traffic analogy.
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|publisher = Linux Journal
|date = 1 December 2006
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