HSD is a refinement of the original Toyota Hybrid System (THS) used in the 1997 to 2003 Toyota Prius. The second generation system first appeared on the redesigned Prius in 2004. The name was changed in anticipation of its use in vehicles outside the Toyota brand (Lexus; the HSD-derived systems used in Lexus vehicles have been termed Lexus Hybrid Drive), was implemented in the 2006 Camry, and would eventually be implemented in the 2010 "third generation" Prius, and the 2012 Prius c. The Toyota Hybrid System is designed for increased power and efficiency, and also improved "scalability" (adaptability to larger as well as smaller vehicles), wherein the ICE/MG1 and the MG2 have separate reduction paths, and are combined in a "compound" gear which is connected to the final reduction gear train and differential; it was introduced on all-wheel drive and rear-wheel drive Lexus models. By May 2007 Toyota had sold one million hybrids worldwide; two million by the end of August 2009; and passed the 5 million mark in March 2013. , more than 7 million Lexus and Toyota hybrids had been sold worldwide. The United States accounted for 38% of TMC global hybrid sales .