Cassette Wells
The number of cassette compartments with their own tape transports in a cassette product.
A cassette well holds one cassette for playback or recording. A single-well deck has one transport; a twin-well deck has two. The count describes available mechanisms, rather than the number of tape sides, heads or recording channels.
Cassette Wells — Cassette Deck
For a cassette deck, two wells can make tape-to-tape copying or successive playback possible when those operating modes are supported. Each well may have different capabilities: one might play only while the other records, or both might support recording.
Compare the functions assigned to each well and the supported dubbing or simultaneous-use modes. Two wells alone do not guarantee any particular combination. In a CD-and-cassette unit, count only the cassette transports; the CD mechanism is separate. The number also says nothing about auto-reverse or recording quality.