There is no repository-side locking in the sense of reserved check-outs. CVS is based on a non-locking copy-merge concept.

However, the CVS server does perform some short-term file locking to serialize repository access for multiple users.

The only locking of files that happens on the CVS client side is in the sandbox: files can be made read-only here to make you (or rather other team members) aware of when you edit a file. If all users behave well and consistently use CVS edit to unlock their files for editing, they can convey to fellow team members that they are about to edit a file or have finished working on it. This works in conjunction with CVS watch. This can help communication and collaboration in a team, but it is not a safe means of knowing exactly what's going on.

See also: Team Collaboration Features.