Content-addressed storage (CAS) is a specialized type of archive that provides the inexpensive and high-capacity storage needed to retain data that, although accessed infrequently, still has long-term relevance to the enterprise. More importantly, CAS provides immutability to data stored in fixed locations on disk (the content address). Archived data cannot be changed once it has been written, and cannot be deleted until the established retention period has expired. This combination of features makes CAS indispensable for organizations concerned with litigation and compliance.