The granddaddy of Version Control Systems* for Unix. Developed by AT&T back in the 1970s, SCCS soon became part of the standard Unix release. Now no longer under any further development, SCCS is part of the public domain. Although most people consider SCCS's syntax awkward and it's feature sets sparse, it is still a widely popular system to use. Because it is in the public domain, many commercial Source Configuration Management packages use SCCS as their basic versioning system Many of the basic features that SCCS first used, and much of its operating principles have been copied by other Version Control Systems*. For example: the concept of checking in and out file from an archive. The use of Keywords* embedded in the source code that get expanded when the file is checked out. The use of locks to prevent two people from editing the same file, and the use of branches for parallel development.