slack space , unallocated space, magic number

slack space

 is refers to portions of a hard drive that are not fully used by the current allocated file and which may contain data from a previously deleted file.

Slack space or sometimes referred to as file slack is the area between the end of a fileand end of the last cluster or sector used by the file in question. Area is an area that will not be used again to store the information there, so the area is "wasted" useless. Slackspace is common in file systems that use a large cluster size, while the file system that uses a small cluster size can organize the storage media more effectively and efficiently.

 

unallocated space

Unallocated space is simply defined as the area or space on the hard drive of the computer that is available to write data to. 

The unallocated space is not viewable to the typical computer user and requires specialized computer forensic software to view and analyze.  Unallocated space can contain deleted files or partially deleted files.

Unallocated space can contain deleted files or partially deleted files.  When a file is deleted, the pointers to the file are removed, but the data remains in unallocated space until such time as the operating system stores another file in the same space, thereby over-writing the data.

Magic Number 

every file system has a signature called a magic number that lows the operating system
to determine its format.