In general terms
Drums - have two shoes mounted inside a round brake drum that press out to stop a car
Disc - have two pads that squeeze a ratationing disk to stop the vehicle
Disc assemblies weight more than drum assemblies
Disc produce drag even when not in use
In general terms Disc are more effective in stopping a vehicle
Jeff Speegle
MCA Shelby Gold Card
http://www.geocities.com/MotorCity/6473
Mustang & Shelby research, documentation
http://albums.photopoint.com/j/View?u=1609818&a=12284202&p=44925357&Sequence=7&res=high.jpg