What is CTAN?

The acronym stands for “Comprehensive TeX Archive Network”, which more-or-less specifies what it's for:

• The archives offer a comprehensive collection of TeX resources.
• The content is made publicly accessible, via the internet.
• CTAN is a network of archives, which strive to stay in step with one another.

The basic framework was developed by a TUG working group set up to resolve the (then existing) requirement for users to know on which archive site a particular package might be found.

Actual implementation offers three distinct types of host:

• Core: Perform management functions as well as serving files to mirrors ;
• Mirrors: Take regular copies of core archives, and serve them to users ;
• Selector: A meta-service, which routes requests to an apparently “local” mirror (“local” is determined by an algorithm that uses your net address to determine where you are, and then selects a mirror that's close).

Note that there is nothing to prevent any archive from supporting other functions, so a CTAN mirror may also operate as a CPAN (Perl) mirror and as a SourceForge (general free software) mirror, and …

Functions carried out by the core archive are:

• Uploads: users may submit new (or updated) material
• Notifications: Significant changes to the archive are reported via the mailing list ctan-ann@dante.de
• Catalogue maintenance
• Mirror monitoring

Users may make direct contact with the CTAN management team.

Users should ordinarily download material from CTAN via the archive selector: this uses the mirror monitor's database, and uses the caller's geographical location to offer an efficient choice of “sufficiently up-to-date” mirror site for you to connect to. This procedure has the advantage of distributing the load on CTAN mirrors.

Before CTAN there were a number of people who made some TeX materials available for public download, but there was no systematic collection. At a podium discussion that Joachim Schrod organized at the 1991 EuroTeX conference, the idea arose to bring together the separate collections. (Joachim was involved because he ran one of the largest ftp servers in Germany at this time and had heavily modified the basic tool mirror.pl for this purpose.)

CTAN was built in 1992, by Rainer Schoepf and Joachim Schrod in Germany, Sebastian Rahtz in the UK, and George Greenwade in the US (George came up with the name). The site structure was put together at the start of 1992 – Sebastian did the main work – and synchronized at the start of 1993. The TeX Users Group provided a framework, a Technical Working Group, for this task's organization. CTAN was officially announced at the EuroTeX conference in Aston, 1993.

(Note: the familiar Perl archive, CPAN, is based on the CTAN model.)

The US site has moved twice. First, after being at Sam Huston State University under George Greenwade, in 1995 it went to UMass Boston where it was run by Karl Berry. Then, in 1999 it moved to Saint Michael's College in Colchester, Vermont, where it was maintained by Jim Hefferon. In 2011 it left the core CTAN sites.

The UK site at Cambridge has been sponsored by the UK TUG, and was managed by Robin Fairbairns. It left the core CTAN sites in 2015.

Sources:

• What is CTAN?
• What is CTAN?