or on the internal.
or the internal?
If the latter, it should already be formatted as OS X Extended (Journaled)
Yosemite should also format the disk for you but if it doesn't, then open Disk Utility and move on.
That said, open Disk Utility and find the HD you are trying to format in the left hand column.
Select the actual name of the HD and NOT the friendly name that appears under it. For example, I have a 1 TB HD which DU shows as 1 TB WDC WD1001FALS-403AA0 Media. Underneath that, and indented appear two more disks called Macintosh HD and Bootcamp. These are partitions on the main volume.
I would select the one with the long name, click on Partition in the right hand window, enter a name for the partition. Note the default is (Journaled) for the format. Select 1 partition under Partition Layout.
Select GUID under Options and then hit the Apply button.
THIS WILL DELETE ALL THE INFORMATION CONTAINED ON THIS DISK. IT WILL END UP AS AN EMPTY DISK.
P
I just received a used iMac (mid2009) Snow Leopard 10.6.8 is installed.I'm trying to download Yosemite OS X. I am getting a message that says I need to format my disk as OS extended(journaled). I cannot figure out how to use Disk Utility to do it.

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