you might have the index service running and if so do this:
Go to start, right click on My computer and then, right click on the C: drive and select Properties. Uncheck the box that says "Allow Indexing Service to index this disk for fast file searching".
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check in scheduled tasks, do you have any tasks running??
be sure to click on the Advanced button and select to show hidden tasks
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Bring up the Task Manager, by pressing Ctrl-Alt-Del simultaneously. Select the Processes tab. From the menu at the top of the Task Manager display, click View -> Select Columns..., check the "I/O Reads" column and click OK. Then, in the Processes display, click on the column header for the "I/O Reads" column to sort the list of displayed processes based on the number of "I/O reads"(The number of read input/output operations generated by the process, including file, network, and device I/Os). Clicking on the column header is like flipping a toggle switch; each time you click, the sort (display) order is reversed based on the values in that column (highest to lowest, or lowest to highest).
read the link below for a further description of task manager with this option used:
http://www.watchingthenet.com/identify-processes-that-cause-high-disk-activity-in-windows.html
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another cause might be not enough memory, go to start, right click on my computer, choose properties
and on the general tab How much ram is listed??
I have 2gb, running xp pro, fully updated and even though my antivirus uses the most I/O's (2 to 3 hundred thousand) I do not hear my hard drive constantly running.
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also in my bios (I have a Dell dimension 3000) I have a setting on the hard drive for quiet or best performance, it was 50/50 either way I set it so I left it at the default, but check your bios to see if you have a quiet setting.
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Let me know if any of this helps.
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