A hard drive works on the same principals as a floppy disk drive. A magnet can polarize parts of a disk to represent data and later read them and translate the data back. The big difference with hard drives is that a disk has one disk to read and write to. A hard disk can have several. Also as the names hard disc and floppy disc suggest, the hard drive disks are made out of higher quality materials so they can be read/written to more frequently. It is these factors that allow some hard disks to hold several Gigabytes of information, as opposed to a floppy's (approximately) 1 Megabyte. For a better look at hard drives consult the Virtual Macintosh stored on this web site. I've set up a link to the VR Page that you can activate by clicking here.