A solid archive is a RAR archive packed by a special compression method, which treats all files, within the archive, as one continuous data stream. Solid archives are supported only by the RAR archiving format, ZIP archives are always non-solid. The archiving method for RAR archives is a user selectable option and may be Solid or non-Solid.
Solid archiving significantly increases compression, especially when adding a large number of small, similar files. But it also has a few important disadvantages:
Solid archiving is preferable if:
Usually files in a solid archive are sorted by extension. But it is possible to set an alternative file order using a special file, rarfiles.lst.
Volumes and self-extracting archives (SFX) may also be solid.
See also: switch -S, switch -DS, rarfiles.lst