The Chicago Bulls broke the NBA record for most victories in a season during the 1995-96 season. The question is, whose record did they break?
Prior to that, the record for most number of wins in a single NBA season was held by the Los Angeles Lakers team for the 1971-72 season with 69 wins. Conincidentally, the Bulls recorded 69 wins in the 1996-97 season as well.
The top 10 list for total number of wins in a season can be found here.