Microsoft confirmed today that players who wish to access the multiplayer component of Halo 4 will need access to 8GB of storage space on their Xbox 360. That can be either on an official Xbox 360 harddrive or on removable flash memory.
However, this will leave some Xbox 360 owners out in the cold, with Core, Arcade, and 4GB console owners left to find more data storage in order to play online.
It will even spell trouble for launch day Xbox 360s (the few that are still left) as freeing up 8GB of space on a 20GB drive is pretty difficult, and essentially renders your HDD into a Halo 4 accessory.
Halo Reach also had a installation requirement, however that was only for Firefight and cooperative play. After release, 343 Industries patched the game to remove the requirement.