Music Media Eras...some help please

Two part question:

1. What would you identify as the major music media of the twentieth century? (Ex. 78s, cassettes, cds)

2. If you had to pinpoint an era (in years) for each media type, what would it be? (Ex. Cassettes 1970-1984??)

I appreciate your help. Any links that may provide evidence for your date choices would be appreciated.