Why is it so easy and quick to accidentally move a file when copying takes so much longer?

The accidental move

We've probably all done it at one point or another: in Windows Explorer, click a file, hold the mouse button down, and drag the file's icon to a new location where we release the mouse button to move the file there.

Except that somewhere along the way, we accidentally release the mouse button and all of a sudden - *poof* - the file is moved ... somewhere. Wherever the mouse pointer happened to be when we unintentionally released it.

Type CTRL+Z.

Or type the ALT key, click the Edit menu and click Undo, if it's not grayed out.

Windows Explorer has an "Undo", and in many cases, it'll undo that accidental move just as quickly as it happened.

Moving a file (single drive)

A move, as its name implies, moves a file from one location to another.

If you drag and drop a file to another location on the same disk drive the default action is to move the file.

When moving to a new location on the same drive, the file's data doesn't actually have to be moved. In this case, a move operation is simply a change to the drive's directory or file listing.

• The directory of the target folder is updated to include the file being moved in.

• The directory of the folder where the file used to reside is updated to no longer list the file.

That's it. And because the actual contents of the file are never touched, it's pretty quick.

Now, that only applies to a file being moved to a new location on the same drive. When we're moving across drives, things get slightly more complicated.

But first, we need to understand how Copy works.

Copying a file

If you drag and CTRL+drop (hold the CTRL key while dropping) a file to another location, the action is to copy the file. A true copy copies the contents of the file.

• The file contents are copied, in full, to some location on the target disk drive. Depending on the size of the file, this can take some time.

• The directory of the target folder is updated to include the new file copied.

That's it. You start with one file and you end up with two identical copies.

Moving a file across drives

If you drag and drop a file on one drive to another, the default action is to copy the file, as I've just described. If you hold down the SHIFT key when dropping, however, the file will be moved. When moving a file from one drive to another - say from C: to D: - elements of both move and copy are involved.

• The file contents are copied in full to some location on the target disk drive.

• The directory of the target folder on the target drive is updated to include the new file copied.

• The directory of the source folder where the file used to reside is updated to no longer list the file. This causes the actual data for that file on the source drive to be released and marked as unused space.

While both are technically "move" operations, a move from one location to another on the same drive will typically be nearly instantaneous, whereas a move from one drive to another will take noticeable time because it actually has to copy the file contents from one drive to another.