When a file is deleted from a computer it is not actually deleted permanently as many believe and this also applies if you proceed to empty the “Trash”. This is because, even if it is no longer possible to see the document in the position it was in before, a copy still exists on your hard drive and will physically remain there until the portion of the disk that hosted the data is overwritten with new information. For this reason, recovering a deleted file is a potentially feasible operation (with specific recovery software), especially if not much time has passed since its deletion. If a file has been overwritten it becomes very difficult to recover, and in some cases impossible. In these cases the only safe method to recover your files unchanged is to have a backup copy.
Where deleted files go and when they are overwritten
Any file is created by bit of information (in computer science the bit would be the fundamental unit, a binary digit made up only of 0 and 1). When it is deleted, all the bits that make up the file are not physically deleted and continue to contain the information that actually constitutes the file.
The operating system (i.e. the basic software that actually makes the hardware work) it does not physically delete the deleted filebut very simply marks it as free space. In this phase, what is simply deleted is the link between the name of the file and its contents: it is as if the operating system lost the “coordinates” to find the point on the disk where the file is located, but the document still exists .
When you create new files, they may be saved on any partition of free disk space. When the storage space previously allocated to the deleted file is seen by the operating system as “free”, it may be used to store new files. It's only at this moment that the contents of the deleted original file are overwrittenin the sense that the portion of the disk that hosted the deleted file is rewritten with other data, making it more complicated (if not impossible) to recover what has been deleted.
How to recover files deleted by mistake and how to delete files permanently
The fact that a file is not overwritten the moment it is deleted is good news if you need to recover it (perhaps because you deleted it by mistake). For recover files deleted by mistake it is necessary to use special software which usually examines the contents of a file system (i.e. the structure used by the system to organize and arrange data in a memory unit) by searching for any deleted physical connections and checking the areas occupied by the data to which they refer. They then copy the contents and, if possible, even reconstruct the parts of the document that have already been overwritten.
What can we say, however, about thepermanently delete files? In this case, if for some reason (for example related to privacy) you want to overwrite the document to be deleted as soon as possible, special software can be used for this purpose which generally overwrites the contents of a file several times before delete it or overwrite all the “free areas” of a file system, so that the deleted document can no longer be recovered.
