The Data Disk is an orange floppy disk.
The Date Disk is used by Sir Grodus to store important information in. TEC, wanting to know more of Grodus' plans, sends Princess Peach to retrieve it during the intermission of Chapter 5. Peach much head into Grodus' room while invisible (to avoid Grodus' goons) and insert the Date Disk into Grodus' computer allowing TEC to freely view the information. Peach then puts the Data Disk back onto the shelf to make it appear that it was never been used.