In 1968, recorded music sales hit $2 billion worldwide, with about half of that being in the United States. Of the sales, 60% went to LP albums, 30% to single disks (45s), and 10% to tapes (including 4-track, 8-track, and cassette).
1968 was a turning point for the cassette format. It was the first year that cassette player sales surged past 4-track and 8-track equipment sales. Further, cassettes player sales were set to move past record players within five years.
A new format was introduced in 1968 that you may have never heard of: The Pocket Disc. It was introduced toward the end of the year as a truly portable format. It was 4 inches in diameter and sold for 49 cents. The idea was that you could put it in your pocket and take it with you to play at a friend’s house. It would play on a standard turntable (so long as it wasn’t one of the automatic ones) or you could purchase a smaller version of the turntable to play these discs. They even sold the discs in vending machines. However, this was a short-lived fad–passing into oblivion after only a couple of years.
Because of the short life of this format, I have not been able to find a lot of other information. The discs are extremely rare and go for hundreds of dollars now.