How do I find out which processes are causing the most disk activity?

Perhaps enabling the I/O reads and writes in the task manager (ctrl+shift+esc). When looking at the processes in task manager select View then Select Columns. Look for the I/O read optiona nd I/O write option and click them.

This is what I get:

While I prefer the accepted answer, there is another way with the existing task manager.

• Task manager > Performance (tab) > Resource Monitor (button) > Disk (tab)

I like the freeware Process Explorer. It provides a bit more detail than the Windows Task Manager, including per-process I/O graphs. Great for immediately spotting processes doing a lot of disk I/O.