The Difference in a CD-R, DVD-R & a CD-RW

by Bert Markgraf Google

    Most desktop PCs and many laptops have optical drives that can read and write to various types of CDs and DVDs. To choose the type of disc that's best suited for your application, you have to match the data you want to store to the characteristics of the disc. Some work best for the permanent archiving of movies while others quickly and inexpensively store small files. It is a good idea to make backup files of software, and sometimes you have to back up files that change often. CDs and DVDs can handle these jobs effectively, but you have to buy the right type.

    Capacity

    While CDs and DVDs use the same materials and technology, DVDs are a more recent development that places two thin CDs together for greater storage capacity. Depending on how tightly the reading and writing lasers place the spiral reading pattern on the disc, a CD-R or CD-RW can store 550MB, 650MB or 700MB. The last two are the sizes usually available in stores. The storage capacity of DVDs depends on how many layers they have and whether they are single-sided or double-sided. A single-sided single layer DVD can store 4.7GB. A double-sided DVD can store twice that at 9.4GB. A single-sided DVD with two layers can store 8.5GB.

    Reusability

    CDs and DVDs can be either recordable only or rewriteable, depending on the type. The "R" in CD-R and DVD-R stands for recordable and means that you can write your data to the disc once only. It can't be changed once recorded, although you can read the data many times. When a disC has an "RW" in its name, it stands for rewriteable. That means you can use the disc again after recording something and it will store the new data.

    Longevity

    Manufacturers distinguish between three types of lifespan. They estimate the shelf life of optical disks to be five to 10 years. You can rewrite RW discs up to about 1000 times and, once recorded, they remain readable for between 20 and 100 years. Recordable discs remain readable between 50 and 100 years. Manufacturers base these claims on accelerated aging tests that try to simulate real conditions. Actual life spans may differ from these claims and depend on the materials used in the manufacture of the disc and storage conditions.

    Speed

    Reading and recording speeds of optical disks are based on the original playing duration of an audio CD. A typical 76-minute audio CD took 76 minutes to play -- and 76 minutes to record at a speed of 1x. Today's drives and discs support speeds up to 48x. When the speed is marked on the disc package, you should record at the marked speed or lower for best results, even if your optical-disk drive can support higher speeds. You can set the recording speed in the recording software to match the speed recommended for the disc.

    About the Author

    Bert Markgraf is a freelance writer with a strong science and engineering background. He started writing technical papers while working as an engineer in the 1980s. More recently, after starting his own business in IT, he helped organize an online community for which he wrote and edited articles as managing editor, business and economics. He holds a Bachelor of Science degree from McGill University.

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