How can I find out what is using the hard disk? [duplicate]

Possible Duplicates:
hard drive activity by program?
What is causing hard drive grinding?

Once or twice a day my computer starts writing significantly hard to the hard drive, the HD led is ON and the performance hit is noticeable. A strange observation is that the Task Viewer does not show I/O activity - even Process Explorer shows no CPU activity and no I/O bytes read or written.

Is there a way to know which application is using the hard drive and how much data is it reading or writing?

Windows 7 and 8 has a nice and improved Resource Monitor that shows some nice stats about the current disk activity.

I find it really strange that Process Explorer is not showing it. It should show all processes, normally, and you should see the culprit in it.

Try eventually with Process Monitor. It will be more messy and will require filtering, but at least you should find for sure what is using your hard-drive.