ben's SCM page

Source code management (SCM) and version control (VC) systems:

• RCS - version control for individual files. Like SCCS but represents history as a series of diffs. No remote access.
• SCCS - version control for individual files. Like RCS but represents history as a list of lines and which versions they are present in. No remote access. GNU has an implementation called CSSC
• CVS - version control for trees of files. An old classic that everybody loves to hate but is the de-facto standard for open source software development (though in the past year or so that has slowly been changing as other systems become usable). Central repository. Poor support for working offline (wrt to the central repository). Branching is slow and lame. Use RCS-like data file format (with some extra metadata). Network connectivity over own protocol (for anonymous access) or rsh-like protocols (eg ssh). Each checkout has no history - need to consult central repository for that.
• darcs - written in Haskell by a physicist, but apparently ok despite that. I've used it a little for 'msnlib' development.
  Based on a theory of patches, where abstract patches introduce some kind of change and have possibly many concrete representations. Repo format is a set of representations of patches that when all applied to the empty repository give the head version. distributed/offline working. push/pull/mail. Each checkout has full history. Branches supported by creation of entirely new repository by cloning existing one (this is also one of the ways that git can be used).
  A Google search for 'darcs patch theory' found (at time of writing) quite a nice selection of links.
• GNU Arch - dunno much; distributed/offline working(?)
• subversion (SVN) - dunno much. doesn't seem to support distributed development.
  The O'Reilly SVN book is available online. Explicitly created to be an improved CVS, rather than
• git - my favourite at the time of writing - centred mostly on the linux development community. distributed/offline working. repo format is content-addressable hash table thingy with entries being commits, trees, files. push/pull/email. Network connectivity over own protocol (for anonymous access) or rsh-like protocols (eg ssh) or http. Each checkout has full history. The suite is implemented in a bunch of different components, git being the core and others such as cogito and stgit adding more functionality. I'd recommend looking at cogito as the place to start (eg. apt-get install cogito) if you know nothing about git and want to do version-control things with it. I have a few notes on another page.
• BitKeeper - what the linux kernel community used to use. There was eternal license-related flamewar. Abandoned in favour of git. distributed/offline working. push/pull (?mail).
• Mercurial - don't know much about this

I've become more interested recently in open source development process. I've kept half an eye pointed at the linux (kernel) project since about 1996 and sent in occasional patches for other bits of software; the Globus Toolkit was the first big project that I work intensively on and for that I'm still keeping an eye on globdev, part of which is attempting to open up the development process a little bit more.

Exposure to stg and darcs have altered my way of thinking about distributed open source development, to have a lot more respect for patches, and for the idea that work should be presented as a (possibly singleton) series of patches that elegantly describe the work.

Something that's interesting perhaps is that its a combination of technical issues and social issues, tied closely together (for example, the choice of SCM can strongly influence the development workflow in adverse ways (a pet peeve being centralised repositories)).

Wikipedia has a List of revision control software.