From Wikipedia:
In 1992 Cannondale introduced the 2.8 series frame based on CAD (computer aided design) and finite element analysis to make a frame weighing only 2.8 lbs. The 2.8series featured a tapered large diameter down tube, double-offset bottom-bracket cluster, ovalized top-tube, and double-butted seat tube to achieve the weight reduction. The same year the 1.25" Sub One all aluminum fork was introduced. [SUP][13][/SUP] [SUP][14][/SUP]
Cannondale marketed subsequent frames with the CAAD designation (for "Cannondale Advanced Aluminum Design") which first appeared in their mountain bike frame series. In 1997 the CAAD3 road frame was introduced featuring most of the design from the 2.8series.[SUP][15][/SUP] The CAAD4 model introduced S-bend aluminum seat stays for improved comfort.