[KzooKid]

I can't prove it, but I have a theory for the 4th song is best idea:

For those of us who remember the cassette tape days, finding a song on a cassette was difficult. If you wanted to play the 3rd song on the tape, you fast forwarded, then randomly hit play. You ended up halfway through the 2nd song, so you fast forwarded again. Now when you hit play you were on the 5th song. This frustration was relieved when CD's came out.

I've looked at some old tapes. Most of the "singles" from an album are in the middle of the tape. The theory is that you will listen to the rest of the tape to hear that "Singles" on the album.

So let's say that there are 10 songs on a tape, usually 5 on each side (unless a song is really long. Then you would have 4 and 6 respectively.) Track 1 and 2 are songs on the album 3 and 4 may be hit singles. Track 5 rounds out the side. 6-10 probably follow the same pattern.

This notation gets people to listen to the rest of the songs on the album.

This don't apply anymore since we can by single tracks or hit the skip button on our CD/MP3 players.