The compressed ROM/RAM file system (or cramfs) is a free (GPL'ed) read-only Linux file system designed for simplicity and space-efficiency.
In 2013, Linux maintainers indicated that cramfs was made obsolete by squashfs,[1] but the file system got rehabilitated in 2017 for use in low-memory devices where using squashfs may not be viable.
[2] Files on cramfs file systems are zlib-compressed one page at a time to allow random read access.
The metadata is not compressed, but is expressed in a terse representation that is more space-efficient than conventional file systems.
The file system is intentionally read-only to simplify its design; random write access for compressed files is difficult to implement.