Windows generates short file names from long file names in the following manner:
Note that if a folder or file name contains a space, but less than eight characters, Windows still creates a short file name. This behavior may cause problems if you attempt to access such a file or folder over a network. To work around this situation, substitute a valid character, such as an underscore (_), for the space. If you do so, Windows does not create a different short file name
For example, "Afile~1.doc" is generated from "A file.doc" because the long file name contains a space.
No short file name is generated from "A_file.doc" because the file name contains less than eight characters and does not contain a space.
The short file name "Alongf~1.txt" is generated from the long file name "A long filename.txt" because the long file name contains more than eight characters.