How does CVS differ from RCS?

CVS uses RCS to do much of its work and absolutely all the work of changing the underlying RCS files in the Repository. RCS comprises a set of programs designed to keep track of changes to individual files. Of course, it also allows you to refer to multiple files on the command line, but they are handled by iterating over individual files. There is no pretense of coordinated interaction among groups of files. CVS's main intent is to provide a set of grouping functions that allow you to treat a collection of RCS files as a single object. Of course, CVS also has to do a lot of iteration, but it tries its best to hide that it is doing so. In addition, CVS has some truly group-oriented facets, such as the modules file and the CVS administrative files that refer to a whole directory or module. One group aspect that can be a bit confusing is that a CVS branch is not the same as an RCS branch. To support a CVS branch, CVS uses "tags" (what RCS calls "symbols") and some local state, in addition to RCS branches. Other features offered by CVS that are not supported directly by RCS are 1. Automatic determination of the state of a file, (e.g. modified, up-to-date with the Repository, already tagged with the same string, etc.) which helps in limiting the amount of displayed text you have to wade through to figure out what changed and what to do next. 2. A copy-modify-merge scheme that avoids locking the files and allows simultaneous development on a single file. 3. Serialization of commits. CVS requires you to merge all changes committed (via "update") since you checked out your working copy of the file. Although it is still possible to commit a file filled with old data, it is less likely than when using raw RCS.