Subversion was designed with an abstract network layer. This means that a repository can be programmatically accessed by any sort of server process, and the client “repository access” API allows programmers to write plugins that speak relevant network protocols. In theory, Subversion can use an infinite number of network implementations. In practice, there are only two servers at the time of writing.

Apache is an extremely popular webserver; using the mod_dav_svn module, Apache can access a repository and make it available to clients via the WebDAV/DeltaV protocol, which is an extension of HTTP. In the other corner is svnserve: a small, standalone server program that speaks a custom protocol with clients. Table 6-1 presents a comparison of the two servers.

Note that Subversion, as an open-source project, does not officially endorse any server as “primary” or “official”. Neither network implementation is treated as a second-class citizen; each server has advantages and disadvantages. In fact, it's possible for different servers to run in parallel, each accessing your repositories in its own way, and each without hindering the other (see the section called “Supporting Multiple Repository Access Methods”). Here's a brief overview and comparison of the two available Subversion servers—as an administrator, it's up to you to choose whatever works best for you and your users.