Files of extension 1 can find various applications, here are some of
them:
File Splitter
The file extension 1 is used, in principle, by the File Splitter software
to assign a number to a volume of a divided file.
File Splitter is an application for Windows that allows you to either
automatically divide or join the different parts of a large file into
smaller and more manageable parts, in order to share them.
This being the case, when a large file is created and the user wants to
split the file into smaller volumes, then file extension 1 is given to the
first file in the split file.
Mozilla Firefox
In some cases, Mozilla Firefox will also use the extension 1, giving it
to files that store data about cookies, images, and pop-up permissions.
Mozilla Firefox is a free and open source web browser developed by
Mozilla Corporation.
Unix
In this section, a file 1 is a manual page used by the Man utility, a
Unix program used to view user manuals.
Man is a Unix-based systems tool used to document and learn about
commands, files, system calls, etc., on a GNU / Linux operating system.
This being the case, file extension 1 contains level 1 user manuals
stored in plain text and separated into several segments and delimited by
standard markers.
Since Unix man pages are stored in plain text format, they can be created
and edited with any text editor, for example GNU Emacs.