They are small patches for the game, and big patches for the system. Since Sony is a good company, they add lots of new features to their games :)
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I've got a XBOX Premium and it's never once RROD.
If it has a 20GB hard-drive, then it's most likely premium.
I have RRoD a few times but most is just to do with the power supply, i ordered a new one yesterday.
Mine i got rrod after 1 year and 4 months of getting the xbox. Sent it away on friday