I read this about the revised iMacs; "Removing the logic board from the iMac, iFixit found that the 21.5-inch model features an empty PCIe SSD slot, which means that it could very well be expanded if a user chose to do so. The 27-inch model also features this empty slot." What would you, Could you put in this slot?? I am not really sure how it could be used (low computer experience). Please tell me all that it could be used for.