Version control has been around as long as writing has been around. In print, this existed as the numbering of different book editions. However, version control became much more complicated when the era of computing began. Software developers needed a way to work simultaneously on the same project, while also keeping previous versions in case newer versions contained bugs. Thus, the version control system (VCS) was born.
Git was developed in April 2005 after Larry McVoy withdrew free use of BitKeeper, the VCS that the Linux kernel community had been using. (Note: BitKeeper was originally proprietary software but has been released as open source software as of May 9, 2016). Linus Torvalds, creator of Linux, decided that none of the current free VCSs met his needs for performance. He wanted to design a system where:
-
patching would take no more than three seconds
-
workflow would be distributed
-
there would be very strong safeguards against corruption.
Development began on April 3, the project was announced on April 6th, and it became self-hosting on April 7th. The first merge of multiple branches happened on April 18th. In July 2005, Linus handed over maintenance of the Git project to Junio Hamano.
Since then, Git installations have skyrocketed and many users have switched over from other VCSs.
Today, Git is by far the most widely used VCS. However, there are various other systems with different benefits. This is by no means an exhaustive list, but here are a few alternatives to Git.
Before we dive in to alternatives, let's talk about some characteristics of Git. Git is a free open source distributed version control system. Unlike its predecessors, branch operations are fairly cheap. It uses a distributed (peer-to-peer) model and full history trees are available offline. Git works very well for many developers working on the same project, but is not necessarily the best for single developers. While powerful, the learning curve for Git is steep. In addition, there is limited Windows support compared to Linux.
Currently Used By: Intel, Netflix, Yahoo, GitHub
CVS has been around since the 80s and is considered one of the most mature version control systems. It was released under the GNU license as free open source software. However, there has not been a new version released since May 2008. Several factors account for its fall from popularity. In CVS, moving or renaming a file, or changing a file connected via a symbolic link does not register as a change; both of these actions are recognized by Git as a change. In addition, commits are not atomic, and branch operations are expensive.
SVN is another free, open source software, released under the Apache license. SVN improves upon CVS with atomic operations and cheaper branch operations. However, compared to other VCSs, it is still slow and doesn't have as many repository management commands. It is important to note that SVN is server-based rather than peer-to-peer, which may work better for some situations than others. It does not fix the bugs that CVS had with renaming files and directories.
Currently Used By: LinkedIn, Atmel
Like Git, Mercurial uses a distributed model and branching is relatively inexpensive. Many developers chose Mercurial over Git because of the similarities it shares with SVN, and because it has better support for Windows users. Because Mercurial is implemented primarily in Python rather than C, it is also easier to add extended functionality.
Currently Used By: Bitbucket, OpenOffice
Versions are usually identified by some number/code, a timestamp, and the person who made the change.
Ex: "Version control lets the user compare versions, revert to a previous version, or merge versions."
Software where the original source code is available to be redistributed and modified.
Ex: "I believe in open source software, like Linux."
Software that is owned by an individual or company. There are usually restrictions to use and source code is often kept secret. Proprietary software that comes free of charge is called freeware.
Ex: "macOS is proprietary software - that's why building hackintoshes is illegal."
There exists a single central repository that each client synchronizes with.
Ex: "Gmail is a server-based application."
Each client holds a complete repository and synchronizes by exchanging patches peer-to-peer. This is an example of a distributed system.
Ex: "Napster was one of the first major peer-to-peer applications."
Operations whose changes are rolled back if they are somehow interrupted before completion. This helps prevent source corruption.
Ex: "The SQL standard requires database operations to be atomic."
A collection of commits, and branches and tags to identify commits.
Ex: "I wanted to be able to access it from home, so I pushed it to my Github repo."
Given a version number MAJOR.MINOR.PATCH (e.g. 2.0.6), increment the MAJOR version when you add any backwards incompatible changes, the MINOR version when you add backwards compatible features, and the PATCH version when you make backwards compatible bug fixes.
Ex: "Based on the semantic versioning, I can tell that the new version of Ruby isn't backwards compatible."