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Why some Windows process stay writing on disk even on system idle?

When I don't use my computer (idle), I start to hear my SATA disk very well. But when I use the computer, disk isn't so loud. It's funny but my computer is louder when I don't use it at all. Also "System idle process" is using more CPU on idle.

Question: what Windows 7 is doing when I don't use computer.

Note: no applications running in background.

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marked as duplicate by Diogo, studiohack Sep 27 '11 at 19:27

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There can be many things running in the background while the system is idle. But first, System Idle Process is used to show you that nothing else is eating up the CPU and is set to the lowest priority.

Things that may be running while the system is not being used that can cause the disk to pick up... AV software is one. Another especially under Windows 7 is the defrag utility, it now runs automatically on it's own albeit usually at a predefined time of day.

you could use tools like Filemon etc from Systernals or use the built in Perfmon to start monitoring your system.

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Since CPUs must always be doing something, the "System Idle" process is the CPU twiddling it's thumbs when it has nothing to do.

The list of processes in Task Manager represent a significant amount of other activity. Windows and third-party drivers are perpetually busy with petty housekeeping, monitoring, broadcasting and a hundred other things.

To find out more you can look at network traffic with something like wireshark and look at disk activity with SysInternals utilities.

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