Science, Tech, Math › Science What CDs Are Made Of Print PHOTOSTOCK-ISRAEL/SCIENCE PHOTO LIBRARY / Getty Images Science Chemistry Basics Chemical Laws Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. Learn about our Editorial Process Updated on July 02, 2018 A compact disc or CD is a form of digital media. It is an optical device which can be encoded with digital data. When you examine a CD you can tell it is mainly plastic. In fact, a CD is almost pure polycarbonate plastic. There is a spiral track molded into the top of the plastic. The surface of a CD is reflective because the disc is coated with a thin layer of aluminum or sometimes gold. The shiny metal layer reflects the laser that is used to read or write to the device. A layer of lacquer is spin-coated onto the CD to protect the metal. A label may be screen-printed or offset-printed onto the lacquer. Data is encoded by forming pits in the spiral track of the polycarbonate (though the pits appear as ridges from the perspective of the laser). A space between pits is called a land. A change from a pit to a land or a land to a pit is a "1" in binary data, while no-change is a "0". Read More The History of Computer Peripherals: From the Floppy Disk to CDs By Mary Bellis Scratches Are Worse on One Side than the Other Pits are closer to the label side of a CD, so a scratch or other damage on the label side is more likely to result in an error than one occurring on the clear side of the disc. A scratch on the clear side of the disc often can be repaired by polishing the disc or filling the scratch with a material with a similar refractive index. You basically have a ruined disc if the scratch occurs on the label side. Cite this Article Format mla apa chicago Your Citation Helmenstine, Anne Marie, Ph.D. "What CDs Are Made Of." ThoughtCo, Aug. 27, 2020, thoughtco.com/what-are-cds-made-of-607882. Helmenstine, Anne Marie, Ph.D. (2020, August 27). What CDs Are Made Of. Retrieved from https://www.thoughtco.com/what-are-cds-made-of-607882 Helmenstine, Anne Marie, Ph.D. "What CDs Are Made Of." ThoughtCo. https://www.thoughtco.com/what-are-cds-made-of-607882 (accessed April 18, 2024). copy citation