GamesIndustry.biz is reporting that Gran Turismo 4 has a very good start in Japan, with about 635,000 units of its initial 1 million unit shipment sold through in its first week at retail despite being delayed past Christmas. Developed by Polyphony Digital Inc., Gran Turismo 4 continues where Gran Turismo 3 A-Spec left off, offering more cars, more courses, more race modes and online gameplay via the Network Adaptor (for PS2). In offline gameplay, players will have the opportunity to race in an enhanced arcade and simulation mode based upon similar game mechanics from Gran Turismo 3 A-spec.