Content of file resides in blocks on your hard drive. These blocks can be located one by one or in different places of the disk. Locations of blocks for each file recorded in a special system database called Master File Table or MFT. When you access some file, Windows knows locations of it contents just by accessing this database. Note that file may be defragmented and it's content may be spread around the disk.
When you delete a file (after emptying of Recycle Bin) it is not physically removed from the disk. Instead of it, Windows only marks file as "deleted" in the Master File Table. Blocks of "deleted" file become available as free space (still containing content of old file), and Windows can write to these blocks any new data. Content of small files will not placed on the disk's blocks at all, instead of that, small files stored directly in the MFT, for quick access.
This is how Windows OS works.
Anyone can access deleted files simply by marking deleted file as "existing" in the MFT. This will "recover" delete files, no matter when it was deleted - day ago or few years ago. Of cause, if the file's blocks were not overwritten by a new file.
Often, contents of deleted file can be partially overwritten by a new data, and in such case we can only partially restore deleted file.
To restore deleted file you don't have to be a FBI agent. We have a lot of apps on the market that will do it for you in a few clicks.
