More than one program by more than one manufacturer may produce a given file type. For program files, each software program uses its own file types, plus common types such as dll's, to accomplish its tasks. The file extension is usually, but not always, a true indication of its type, e.g., a .doc file is most often a Microsoft Word document. This extension can be easily changed for convenience or secrecy. Discovery is mostly concerned with data files and the information contained within them.
Examples are computer hard disks, floppy disks, magnetic tapes, or ZIP disks.
Tools for reading file signatures identify the true program source even if the file extension has been changed. The file data remains in the slack space until overwritten. This data is the accumulation of what is in the file, on the media label, discovered by the operator, and contributed by the client. Collectively, it represents the real value of examining an electronic file as opposed to its printed version. A physical slice of media.