When people think of CDs they often think of the music business and the progression of musical playback devices. We have seen the record album evolve to the eight track tape, to the cassette tape and then the compact disc, or CD as it is commonly known. CD's are ideal for music, but they are also commonly used in the world of photography as a storage device for images, photos and videos. Many people download their images from a camera onto a CD via their computer. CDs are optical discs that are used to store digital data and even though they were originally produced for audio, they are now widely used for other types of data.
A CD itself is a thin, flat, circular optical disc which is generally made of polycarbonate. The data on the disc can be accessed when a special material on the disc, which is often aluminum, is illuminated with a laser diode from underneath. Many people think CDs are relatively new, but optical discs in one form or another, have been used for recording video for over 40 years now. After the audio CD hit the market over 20 years ago the CDROM (read only memory), which was basically an optical CD was soon to follow.
CD's are available in a few sizes, various formats and assorted memory sizes. They can usually be bought for less than a few dollars each.