More on Optical Drives: (There are some disk drives that combine optical and magnetic ways of storing and reading data, but they are not common).

Optical drives use laser lights to "read" data that has been "burned" or pressed into a disk. We know those disks as CDs (Compact Disk) or DVDs (Digital Video Disk or Digital Versatile Disk). When a computer "reads" data from either a CD or DVD, it shines a laser light into microscopic sized little pits or holes in the disk. The laser light bounces back as a series of pulses that are coded. The computer "reads" those pulses and translates them into sound or video for us. Sometimes you "burn" a CD or DVD. If you produce a CD or DVD at home, your computer has literally burned the microscopic holes into a reflective layer on the disk. When you buy a DVD or CD from a store, almost always the little pits or holes have been pressed into the disk by super-expensive machines in a room called a "clean room". Even a single speck of dust in these rooms can be a big problem. "Pressed" disks cost more to make but they are more reliable and last longer than "burned" disks.