Drive is one of the major characteristics of surfing affected by surfboard fins.  It is the ability to generate speed and move down the line.  Drive converts into speed, power and aerial capabilities.  
The main aspect of the J-Drive fin that has been changed is the base length.  This is the part of the fin that comes in contact with the bottom of the surfboard.  A longer base length results in more water engaging fin at the joint where it meets the surfboard.  The J-Drive fin system has increased that base length so much that it is actually larger than the depth of the fin.  Something rarely if ever seen with surfboard fins.
 
The length of the base affects forward drive.  More length equals more drive but typically this comes at the cost of things like maneuverability and looseness.  To negate these effects the J-Drive team made other modifications.
The second noticeable difference in the J-Drive fin is the cut away section.  This feature allows the fin system to maintain its increased base length while minimizing surface area.  This helps ensure that there is not an excessive amount of hold coming from the fins.  The bigger the surface area of your fin, the more hold you will have but if you have too much you will not be able to release from turns and make use of your drive power.
 
FCS II Compatible
 
Tri Fins
Front
Base: 5"
Height: 4.60"
 
Center:
Base: 5"
Height: 4.60"