Led Zeppelin's fourth and most popular album, technically unnamed but typically referred to as 'IV,' turns forty-two years old today, Nov. 8, 2013.

To celebrate, we've got two exciting features for your enjoyment.

First up, we talk to 'Led Zeppelin FAQ' author George Case and count down 10 things you may not know about the recording of this legendary album. We think even the most well-read fan could find something new about the album here.

Next, we try to pick some of the best and most interesting cover versions of every song from 'IV' for a special video countdown. That's no easy task, as Zeppelin's peers and disciples have recorded dozens if not hundreds of takes on songs from this record.