How files are stored?
No matter you are using computer with a hard drive (usually formatted as NTFS file system or HFS+ file system if you are Mac users) or removable drive (usually formatted as FAT file system) such as memory card or usb drive, those are called storage media. When you save a file to a specific place, the data contained in the file will be saved to the relevant sectors of the storage media. The file system is used to organize how the data will be stored (such as what sectors they will locate) and record the file attributes. Each file or folder on the disk has its own assigned attributes, such as Archive, Hidden, System, Size and so on. For example a file having hidden attribute isn't displayed in Windows Explorer view.
What happen when you delete a file…
When a file is deleted from your computer it is not really deleted. It is simply removed from the directory of files in the folder. Even though you can no longer see the file in the folder, its contents still exist 100% intact at this point. If you're using Windows the file will be moved to the Recycle Bin. If you're a Mac user, it will go to the Trash. As long as a file remains there it can easily be restored in its entirety with no difficulty. So the first thing to do is check the Recycle Bin or Trash. And use the Restore option to make it alive again.
When you empty the Recycle Bin or Shift + Del…
When you empty the Recycle Bin (or Trash) or delete a file using another method (such as Shift + Delete or Command +Delete), the file is still not deleted. Only the file attributes are marked as delete and the space occupied by the file becomes available for re-use by other files. And usually won’t get reused right away depending on how frequently new data are writted.
When you format a drive…
There are two kinds of format: low-level format and high-level format (also called quick format or full format). Generally speaking we regards format as high-level format for low-level format can only be executed after manufactoring. Low-level format will completely wipe everything on the drive while high-level format will only remove those file attibutes, which means the data are still intact there on the drive.
Why and how the deleted files can be recovered?
As long as real data contained in the files remain intact (not overwritten), it is almost certain possible to get those deleted or formatted files recovered. Data recovery software understands the internals of the system used to store files on a disk (the file system) and uses this knowledge to locate the disk space that was occupied by a deleted file. If you are running computer with Windows, Recuva or Pandora Recovery is the program that I recommended. For Mac users, see these totally free Mac file recovery programs.
When the files are overwritten…
When the files are overwritten (space get reused by other files), it is almost impossible to bring them back with data recovery tools. The only option is to send the device which contains your lost files to a technical data recovery company and see if they have any special means to do data recovery. It’s been said IBM ever successfully recovered data overwritten 7 times. So do your best to avoid data overwritten. Do not save more files to the drive where your deleted or formatted, do not modify data, do not damage the drive etc. Better put the drive in a safe place if you want to maximize chances of file recovery.
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