Any file system registers a file by its name in the File Allocation Table (FAT) of a partition, while the file data proper are stored in the sectors of a partition (hard disk) forming a chain. Deletion of files by means of an operating system only deletes a filename from the FAT, while the sectors containing the file proper are considered free. Data may be written to the sectors after deleting the file name from the FAT, but the file data remain intact unless randomly overwritten. Deleting a file name in the FAT does not assure that data will ever be written over that files data sectors on the hard drive.
The Windows operating system, for example, allows users to easily recover a deleted file. There are many popular utilities software products that also serve this purpose.
It is more difficult to recover a deleted file in the Linux operating system. Files and data are bound up with greater complexity in Linux's file systems such as Ext2, Ext3, and ReiserFS. But even under Linux, file data is still stored in disk sectors even after the deletion.
Both off-the-shelf and rather inexpensive software, and a simple hardware device may be used to recover files, data, hard disk controller capabilities and even magnetic microscopy.