Admittedly at first glance, an article on how to use and understand the Trash Can inside of OS X may seem a bit beneath even the most novice of newcomers. However, the Trash Can, and even deleting files in general, both work very differently in OS X than other operating systems. Even I was thrown for a loop or two when I made the jump to OS X. I hope this extensive rundown of the Trash Can will help you better understand and manage your files and storage space on your Mac.
How OS X Handles Deleted Files:
When you delete a file in OS X (that is, empty the Trash Can) the operating system is not actually erasing the data (unless you tell it to, more on that in a bit), but rather it is actually just marking the space that said file took up on the physical hard drive as free space to be written over with new data. This is pretty common file handling across most operating systems.
Each storage device that you plug into a Mac running OS X gets its own Trash Can specific to that device.
Where OS X gets unique with handling files set for deletion is with additional storage mediums such as external hard drives and USB thumb drives. Each storage device that you plug into a Mac running OS X gets its own Trash Can specific to that device. This is done with a hidden folder that is used for storing files on that drive that you have sent to the Trash Can.
Hidden Trash Can Folder On USB Storage Device Containing The Files You've Moved To the Trash Can
The Trash Can icon in the OS X Dock is actually an aggregation of all the deleted files on all plugged in drives on your Mac. It is important to understand that no file is deleted until you empty the Trash Can. Until you do so, the files are in a hidden folder and still using disk space on your various storage devices.
This may seem redundant at first but as it turns out this is a very intuitive way to handle files set to be deleted. A file on a portable USB thumb drive gets put into the Trash Can folder for that USB thumb drive, and stays there until you empty the Trash Can for it by emptying the Dock Trash Can with the device plugged in.
The files you send to the Trash Can will follow the portable device around until the Trash Can is emptied
This is good because the files you send to the Trash Can will follow the portable device around until the Trash Can is emptied. So if you decide that you needed a file you placed into the Trash Can on the Mac at your office, it is there inside the Trash Can on your Mac at home once you plug the USB drive in. No more trips back to the office or waiting until tomorrow to get work done.
Trashed Files Still Eat Up Space
Keep in mind that this means files sent to the Trash Can on an external drive are still using the disk space on that drive until the Trash Can is emptied. So if you have a full USB thumb drive and delete all the files, you do not actually recover the storage space on the drive until you empty the Trash Can with the drive plugged in.
A Big File/Folder Taking Up Space That you Want To Delete
Even After Being Sent To The Trash Can, The File Is Still Using disk Space
Only After The Trash Is Emptied Do you Recover Storage Space
I mentioned that, when you empty the Trash Can, for all intents and purposes the files are gone. However, the data on the physical drive is still there and could potentially be recovered using third party software. It has not been deleted but has been marked for reuse by OS X, and will eventually be written over with new data. If you are ever deleting sensitive data and wish to know that the data has been written over immediately upon emptying the Trash Can; you can do a Secure Empty Trash, which will immediately write the data over on the physical hard drive.
Keep in mind this process can take a few seconds or upwards of an hour depending on the size of the data files being deleted and written over and your hard drive write speed. Also bear in mind that if someone really wants to access the deleted files on your hard drive, say law enforcement, anything short of completely destroying the physical drive can be undone.
Command + Right Click On The Trash Can To Toggle Secure Empty Trash
If emptying the trash seems to take too long, or you want to set Secure Empty Trash as the default behavior; with Finder active go to Finder > Preferences > Advanced Tab and check or un-check Empty Trash Securely.
Set The Default Behavior For Emptying The Trash In Finder
Finally, when you have a disk in the CDROM drive, a .dmg file mounted (OS Xs way of installing apps) or an external storage device and wish to eject it; you can do so by clicking the correct icon and dragging it to the Trash Can icon, which will have turned into an Eject icon.
The Trash Can Turns Into An Eject Icon For CDs or External Storage Devices
OS X is a truly advanced operating system, and because of this some things may work a little differently than at first expected. Once you have a good working understanding of how OS X handles deleted files however, you will see that it is not only a smart way to deal with them, but also a safe way that is sure to eventually save you from a headache. I hope this quick rundown of the Trash Can will help improve your OS X experience as well as help you to better manage and use your storage space when deleting files.