In Mac OS X, why can't I unmount my drive to initialize it?

When you attempt to initialize a disk with Disk Utility, Drive Setup, Apple HDSC setup, Internal HD Format, or a third-party drive formatting utility, you may get an error message resembling this: "Cannot initialize. Cannot unmount drive because a file is in use."

This error means that there is a file in use on the hard drive, and it can't be unmounted. A drive must be unmounted or taken offline before it can be initialized. If the drive is in use for some reason, it cannot be unmounted and thus cannot be initialized.

You should always boot from a drive other than the one you're trying to initialize:

• To boot from a CD, DVD, or a different hard drive, see In Mac OS X, how can I boot from a CD or DVD and/or ignore my startup disk?
  
  
• To boot from a floppy disk, use the Disk Tools disk that came with your computer. Turn off the computer, put the Disk Tools disk in, and restart.

If you are still having trouble unmounting the disk, try the following:

• Try to unmount the drive manually by dragging it to the Trash.
  
  
• Make sure that there are no applications currently running from the disk you want to initialize.

Comments/Questions/Corrections