Just wondering why in Linux gui CPU usage never seems to get down to 0% even when just idling with nothing going on. Depending upon which desktop is being used it seems to hover around 15%-20%.

In windows CPU drops down to 0% when it is idling, why doesn't the same happen in Linux?

The "top" command will show you which processes are running and their cpu usage.

Hi there,

look at the number of background processes that you have, and try to identify the one that consumes lots of CPU time.
They may be sleeping most of the time, but once in a while they wake up and have a few milliseconds' work to do. Swap memory in and out, update the clock display, reply to a network request. That's summing up.

However, on my Linux machines, top shows about 99% idle most of the time, maybe 95% when I move the mouse fast (AMD X2 dual core at 2x2GHz, the Intel Atom based system currently not powered on).

It drops down to 0, alright, but every other second it jumps to about 2% or so, or even around 4..5% when you move the mouse a bit (AMD Sempron 3100+ single core at 1.6GHz).

So the two systems aren't all that different.

[X] Doc CPU

Maybe linux and windows uses different means to measure.

A computer only really goes to 0 when it is fully powered off.

Hi there,

I'm quite sure that's true. Plus, Windows only displays percent with no fractional part, so everything below 1% is displayed as 0, while Linux (the "top" tool) displays tenths of percent.

However, this rounding error isn't that obvious if you ignore the CPU load the Windows task manager displays, and instead look at the CPU% of the idle "process". You'll see that it never goes to 100%, but 99% at most. So the remaining 1% must be other processes taking up less than 1% each, being displayed as 0%.

Either that, or with the CPU in HALT state. :-)

[X] Doc CPU