The CD's design drew inspiration from vinyl records: Like the grooves on a record, CDs are engraved with a spiral of tiny pits that are scanned by a laser - the equivalent of a record player's needle. The reflected light is encoded into millions of 0s and 1s: a digital file.
Because the pits are covered with plastic and the laser's light doesn't wear them down, the CD never loses sound quality.
Legends abound about how the size of the CD was chosen: Some said it matched a Dutch beer coaster; others believe a famous conductor or Sony executive wanted it just long enough for Beethoven's 9th Symphony.
Dischord act Dag Nasty did a song called "Exercise": http://www.allmusic.com/ cg/amg.dll?p=amg&uid=UIDSUB02 0406090452520441& sql=Ap9q8b5m4tsqf If that's not it, try doing the song title search there and see what else comes up.