In OS X, there are two ways to move or copy icons from one place to another: by dragging them and by using the Copy and Paste commands.
You can drag icons from one folder to another, from one drive to another, from a drive to a folder on another drive, and so on. (When you’ve selected several icons, drag any one of them; the others tag along.) As you drag, you see the ghostly images of all the selected icons moving with your cursor. And the cursor itself sprouts a circled number that reminds you how many files you’re moving.
You can tell that the copying is under way even if the progress bar is hidden. A tiny progress bar appears right on the icon of the copied material in its new home. You can cancel the process either by pressing ⌘-period or by clicking the in the progress window.
Understanding when the Mac copies a dragged icon and when it moves it bewilders many a beginner. However, the scheme is fairly simple when you consider the following:
On a single disk, dragging from one folder to another moves the icon.
Dragging from one disk (or disk partition) to another copies the folder or file. (You can drag icons either into an open window or directly onto a disk or folder icon.)
If you press the Option key as you release an icon you’ve dragged, you copy the icon instead of moving it. Doing so within a single folder produces a duplicate of ...