Multi-disc albums are counted once for each disc within the album if it is over 100 minutes in length or is from the vinyl era. For example, each copy of 
The Smashing Pumpkins's 
Mellon Collie and the Infinite Sadness (running time of 121:39), 
OutKast's 
Speakerboxxx/The Love Below (running time of 134:56), and 
Shania Twain's 
Up! (145:44), all 
double albums, were counted twice, meaning each album was certified diamond after 5 million copies were shipped. 
Pink Floyd's 
The Wall and 
The Beatles' 
White Album, both vinyl-era, are also counted double even though their running times are under the minimum requirement