Your hard drive operating system has a file system. That file system uses a table of contents to point to the exact spot (spots) where your file resides. When you just delete a file, all it does is remove where it is indexed in the table of contents and marks the file itself as space that is able to be written over. Until new data is saved, that file is still there, just not indexed. When new data is saved, it writes over some or all the old data and a new index point is written in the table of contents.