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This process uses the copy-modify-merge model, which works as follows: Developer A requests a working copy (a directory tree containing the files that make up the project) from CVS.
This is also known as "checking out" a working copy, like checking a book out of the library. At the same time, other developers may be busy in their own working copies.
Deciding when to update or when to commit is largely a matter of personal preference or project policy.
It turns out, however, that these two functions are closely connected.
Record keeping became necessary because people wanted to compare a program's current state with how it was at some point in the past.
It is part of a larger work entitled This is a set of free, online chapters about using CVS (Concurrent Versions System) for collaboration and version control.
It covers everything from CVS installation and basic concepts all the way to advanced usage and administration.