FAT or File Allocation Table is a computer file system architecture or hard drive format. It was originally designed in 1977 for use on floppy disks before being adapted for use on hard drives in the Microsoft DOS to Windows 9x variants. In modern operating systems FAT has been replaced as the hard drive format of choice in Windows by NTFS since Windows XP due to overall disk size limitations and maximum single file size limits that are not present in NTFS, however FAT is still widely used in removable media such as SD cards and USB thumb drive memory sticks.