Base directory
The so-called base directory is the place where FS-UAE stores its files. By
default, this location is Documents/FS-UAE
or $HOME/FS-UAE
depending on the
FS-UAE version and your system. It it possible to change this location to
something else.
See the directories documentation for more information.
If you use the portable version, the base directory is the same as the portable directory (the directory containing Portable.ini).
Source: https://github.com/FrodeSolheim/fs-uae/blob/master/docs/base-dir.md