either a plain socket or Secure Shell (ssh). Git also has a CVS server emulation, which enables the use of existing CVS clients and IDE plugins to access Git repositories. Subversion repositories can be used directly with git-svn. Efficient handling of large projects Torvalds has described Git as being very fast and scalable, and performance tests done by Mozilla showed that it was an order of magnitude faster diffing large repositories than Mercurial and GNU Bazaar; fetching version history from a locally stored repository can be one hundred times faster than fetching it from the remote server. Cryptographic authentication of history The Git history is stored in such a way that the ID of a particular version (a commit in Git terms) depends upon the complete development history leading up to that commit. Once it is published, it is not possible to change the old versions without it being noticed. The structure is similar to a Merkle tree, but with added data at the nodes and leaves. (Mercurial and Monotone also have this property.) Toolkit-based design Git was designed as a set of programs written in C and several shell scripts that provide wrappers around those programs. Although most of those scripts have since been rewritten in C for speed and portability, the design remains, and it is easy to chain the components together. Pluggable merge strategies As part of its toolkit design, Git has a well-defined model of an incomplete merge, and it has multiple algorithms for completing it, culminating in telling the user that it is unable to complete the merge automatically and that manual editing is needed. Garbage accumulates until collected Aborting operations or backing out changes will leave useless dangling objects in the database. These are generally a small fraction of the continuously growing history of wanted objects. Git will automatically perform garbage collection when enough loose objects have been created in the repository. Garbage collection can be called explicitly using git gc. Periodic explicit object packing Git stores each newly created object as a separate file. Although individually compressed, this takes up a great deal of space and is inefficient. This is solved by the use of packs that store a large number of objects delta-compressed among themselves in one file (or network byte stream) called a packfile. Packs are compressed using the heuristic that files with the same name are probably similar, without depending