These cartridges represent the first step in technologies to automate the reading, writing and retrieval of data. Previous to this, all data had to be retrieved, loaded and dismounted by hand.
IBM 3850 MSS mass storage system (simply known as MSS) was first announced by IBM in late 1974 with data cartridges in form of circular cylinders able to store 50 megabytes of data.
The tape cartridges always worked in pairs so 2 Mass Storage Cartridges = 1 Mass Storage Volume = 100 MB. The cartridges were stored in hexagonal stacks, rather than square, to save space.
The MSS was able to stage out infrequently-used data from disk onto tape as well as bring it back later.
IBM 3850 MSS was introduced at CERN in July 1978 and was in use until July 1989. The driving force was the introduction of CERNET linking the computers on CERN site so users could send data samples to CDC and IBM central computers for storage.
IBM 3850 was primarily used by IBM 370/168 and IBM 3032 mainframes and was seen as extremely reliable right from the start (compared to earlier experience with tape reliability). Towards the end of its life, the data was copied onto 3480 tape cartridges.
See also:
http://library.web.cern.ch/library/content/ar/yellowrep/varia/annual_reports/1978_E_p87.pdf
http://cdsweb.cern.ch/record/1292450/files/n-137.pdf
http://cdsweb.cern.ch/record/1292507/files/n-194.pdf
http://www-03.ibm.com/ibm/history/exhibits/storage/storage_3850.html