In MusicBrainz terminology, a prototypical medium is one of the physical, separate things you would get when you buy something in a record store. They are the individual CDs, vinyls, etc. contained within the packaging of an album (or any other type of release). Mediums are always included in a release, and have a position in said release (e.g. disc 1 or disc 2). They have a format, like CD, 12" vinyl or cassette (in some cases this will be unknown), and can have an optional title (e.g. disc 2: The Early Years).
Note that a side of a disc, like side A of a vinyl, is not its own medium; the whole vinyl disc is. Digital (as opposed to physical) releases don't have "real" mediums, but they should be entered as several mediums if they are officially divided in several "discs". Exceptions in the treatment of mediums can exist: DualDiscs are usually entered as two mediums if the tracklist is the same on both sides, but with different mixes.
Disc IDs are linked to mediums. The content of a medium (which tracks and in which order) is given by a tracklist that is linked to the medium. Tracklists also have a MusicBrainz-specific meaning. A single tracklist can be linked to multiple mediums.
These are mediums of their respective releases.
- CD 1 of the 1984 US release of "The Wall" by Pink Floyd.
- CD 2 of the 2005 UK release of "Aerial" by Kate Bush, named "A Sky of Honey".
- 12" vinyl 1 of the 1975 US release of "Physical Graffiti" by Led Zeppelin.
- And also 12" vinyl 2 of the same release (but not sides A, B, C and D!).
- Digital Media 1 of the 2010 US digital release of "My Beautiful Dark Twisted Fantasy" by Kanye West.
When adding a medium to an existing release, please ensure that year of release does not conflict with the medium being added. Here are the dates of first commercial releases for some common formats:
- 7" records: c.1895
- 10" records: c. 1898
- 12" records: 1903
- Reel-to-Reel: 1954
- 8-Track: 1964
- Cassettes: late 1965
- Compact Disc: October 1, 1982
- SACD: September 1999
- DVD-A: 2000