Final Media Formats used in Mastering:

1/2" & 1/4" analog tapes (with/without Dolby A & SR)
They are considered the best recording media for final mixing, and are preferred by the best recording and mastering studios around the world. In particular, 1/2" analog without Dolby in 30 IPS is considered even better than 96 Khz/24bit Resolution digital mixes.
DAT
The most popular format the last 10 years. Without being an ideal solution, it is a very practical format with acceptable quality.
CD-R
CD-R has become a commonly used format by project studios, particularly since many are using professionals and semi-professionals computers and digital audio workstations to mix their material directly on hard drives. It is the least desirable solution and A-B tests showed that DAT recordings almost always sound better.
CD-R with 24bit data files
If mixing in 24bit resolution process is possible, a CD-R with 24bit data files is a much better solution than 16bit DAT and CD-R because high resolution means higher definition.
Exabyte 8mm Tape
This special tape is the standard in making glass masters in mass production CD's. At Athens Mastering we accept either sound exabyte with DDP protocol, or in archived format for Sonic Solutions. All the material at Athens Mastering is also stored as high resolution exabyte tapes for back-up and for future use in new formats such as DVD and DSD.
Quarter-track tape
Tapes mainly from the 1960's that recorded in both sides can be played in both forward and reverse.
Cassette
It's not a professional solution but is still used if the original and/or essential material has been lost.

Vinyl records 33rpm
Commonly used if the original tapes and/or essential material is not available. If the records are in good condition, NoNoise and other unick methods are used so that it is difficult to distinguish the final processed master from the original one.
Gramophone records 78 rpm
Records from the period 1900-1960. Unique documents transfered to CD's with excellent results, and with the aim of not altering the musical content.
Sony's U-matic 1630 & PCM 9000
Upon agreement, these formats can be used.