In the 1980s it was normal to load and save programs and data on a tape. A normal cassette tape could be used to store data. This was a cheap but slow solution. Loading a typical game took 10-15 minutes. Later fastloaders were available speeding up the process.
The first method to load and save programs on the Commodore 64 was the Datasette.
A modern solution is the Cassiopei v2.0.
For the C16/C116 and Plus/4 Commodore made the 1531.