Rockstar said that the game will need two disks to be playable in xbox 360. One of tem will have the mandatory installation of 8GB of data, if you have the 4GB hard drive Xbox you will ned an extra place to save the data.

It won’t be necessary to change the disc while you are playing.

In Ps3 we won’t have two discs, just one blu-ray, but again we will need 8GB to install the game.