Kingdom Hearts II Kingdom Hearts 2 final mix:Data?

So i've been hearing and watching videos about there being some data system(or something like that).I heard and saw this allows you to fight bosses and whatnot.Well my question is where can i find this data system(again or whtever it's called).Just to make things clear i have Kingdom Hearts 2 Final Mix.

 

It's the very last room in the Cavern of Remembrance.

 

ohh ok.Oh and thnx for the help!!

 

also, if you cleared the game, there should be a golden crown symbol on your save file when you're in the load screen

 

Ok thank you aswell!!!!

 

Also, beat all worlds, (100 Acre wood and Atlantica included) beat the boss (again if you haven't already)

Go to Disney World, and the Hall of Cornerstone.

There, you'll fight the hardest fight of your life.

Seriously.

Spoiler

It's Terra, in his full armor form

Also, I suggest you at least play on Normal, to unlock the final secret trailer in Theater mode.

 

one more thing, to get to the data room, in the cavern of remembrance, you should have all your drive forms, except the limit form, in the max level. it can help a lot if you do. and there is a room that you fight a lot of nobodies, there you should use to peter pan or stich summon. they helped me a lot. right after that room is the data program