Switch -S - create solid archive
Solid is a special archive type. Solid archiving significantly improves the compression ratio at the cost of archive update speed. This switch is meaningful only when creating a new RAR archive.
Shell mode equivalent of this switch is the "Create solid archive"option in the Archive name and parameters dialog.
add all *.c and *.h files from the current folder to the solid archive Sources
WinRAR a -s Sources *.c *.h
Please refer to the Solid archives chapter for further information.