A cassette tape used to store computer date. The Commodore 1530 (C2N) Datasette (a portmanteau of data and cassette), was Commodore's dedicated magnetic tape data storage device. Using compact cassettes as the storage medium, it provided inexpensive storage to Commodore's 8-bit home/personal computers, notably the PET, VIC-20, and C64. A physically similar model Commodore 1531 was made for the Commodore 16 and Plus/4 series computers. (source)