While Gran Turismo 5 does have a mandatory install of 6.4 GB, you can choose between two different methods of performing this install, explains Sony. You can do the typical initial install, which will probably take half an hour or more, or, conversely, you can choose not to do the initial install and start playing straight away. If you do this, the game will install the needed data as you play. Sure, things may be accessed slower at first, but eventually, as the game installs, access times will speed up to the point of what it would be if you just installed the game in full initially.
I'm not a huge fan of mandatory installs - I know from experience it gets quite annoying when you have a small hard drive and have to delete a game's install data just to install another one. Games like God of War 3 and Final Fantasy XIII show us just how much mandatory installs are not needed, loading smoothly and quickly throughout, without any install. However, given the amount of data needed for this title in particular, I can certainly see why Polyphony Digital and Sony opted for this means of lowering the load times that are likely prevalent.
Gran Turismo 5 finally releases next Wednesday, November 24th. This is one day before Thanksgiving, so some of you will have an entire four-day weekend to play. Excited yet?