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UsuallyWindows

macrumors newbie
Original poster
I am trying to erase my Macintosh HD but I keep getting a error saying I can't unmount the disk. I am booting up from the install CD so IDK what the problem is
 
Sometimes it indicates that there's some process using the disk...which is odd but happens.

Search for how to use Terminal to force unmount a disk.
 
Exactly what BrianBaughn says : Check if you have a program still accessing it (anything from finder to 3rd party program to Time Machine encrypting your disk etc).
In activity monitor you can force close a program that can't be stopped FYI.
 
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