The most popular kinds of auxiliary memory used in modern PCs are hard drives and CD/DVD ROMs. But in the long and fascinating history of computing, people have used all kinds of other memory devices, most of which stored information by magnetizing things. Floppy drives (popular from about the late-1970s to the mid-1990s) stored information on floppy disks. These were small, thin circles of plastic, coated with magnetic material, spinning inside durable plastic cases, which were gradually reduced in size from about 8 inches, through 5.25 inches, down to the final popular size of about 3.5 inches. Zip drives were similar but stored much more information in a highly compressed form inside chunky cartridges. In the 1970s and 1980s, microcomputers (the forerunners of today's PCs) often stored information using cassette tapes, exactly like the ones people used back then for playing music. You might be surprised to hear that big computer departments still widely use tapes for backing up data today, largely because this method is so simple and inexpensive. It doesn't matter that tapes work slowly and sequentially when you're using them for backups, because generally you want to copy and restore your data in a very systematic way—and time isn't necessarily that critical