Research into 40 years of changes in the music industry by digitalmusicnews.com shows that the music industry has been in a constant state of change.
In 1973 vinyl accounted for 61.8% of music purchased. 62.7% in 1978. 40 years ago, 8-Track had 14.3% of sales.
Cassette was the dominate format in 1984 with 55% of sales. CD, still a new format, had 2.4% of sales then.
In 2002 CD peaked with 95.5% of all music purchases.
In 2012, CD had dropped to 35.8% of purchases, download albums were 17.1% and download singles were 23%.
All figures are based on Recording Industry Association of America (RIAA) revenue data.