this is a side thing, but every one of these games has a mandatory install (in the background, not like PS3) and so far:
killzone: 40 gigs
call of duty: 49 gigs (PS4)
NBA 2k: 60 gigs (XB1, 50 PS4)
both ship with 500gig internal hard drives. after 9 or 10 games you need to delete something or upgrade. PS4 doesn't support external hard drives, but xbox one doesn't let you swap out he internal one.