Commodore 1530 Datasette
As disk drives were quite expensive, Commodore needed to find a way to have a storage medium alongside its computers that was cheap, inline with its motto “Computers for the masses, not for the classes!”
The Datasettes proved to be just the thing (and also the slowest means of data transfer every made). The Commodore Datasette are just like the C64 etched into our collective memories as everyone who owned a Commodore 64, had a Datasette.
The cool thing was that it could use ordinary music tapes to store programs on.
They encoded their data using digital tones, which sounded like high piched squeels when listened to on a normal tape player, which in turn allowed the copying of programs by means of a dual tape deck, found in most Hifi-sets in the eighties =)