Compact Discs (CDs)
CD-ROM
CDs took over after cassettes tapes. They were first introduced in the early 1980s, and the most common form of compact discs (CDs) are the standard CD-Rom. They are used for many different purposes such as holding data, computer software, and music. They became a popular medium, because as with cassette tapes, they were easy and cheap to produce. Not only could music distributors use CDs, people could too as long as their personal computer has a CD-R drive. This ability to create custom mixes and personal CDs was very much like how cassette tapes were used, but CDs worked differently because they held digital music.
A CD can hold up to 74 minutes of music. According to an illustration by Marshall Brain, founder of How Stuff Works, Inc, the total amount of digital data that can be stored on a CD is "44,100 sample/channel/second x 2 bytes/sample x 2 channels x 74 minutes x 60 seconds/minute = 783,213,000 bytes" ("How CDs Work"). Though this sounds quite impressive, CD are really a "simple piece of plastic, about four one-hundredths of an inch thick" ("How CDs Work" 1). Most of what a CD consists of is an piece of clear polycarbonate plastic which is manufactured with "microscopic bumps arranged as a single, continuous, extremely long spiral track of data" ("How CDs Work" 1). In a way, CDs are an updated and smaller version of vinyl records, because when vinyl records are made, the metal master has grooves put into for the stylus or needle to read. The bumps are covered with a reflective aluminum layer, and the CD is sprayer with a "thin acrylic layer...to protect it" ("How CDs Work" 2). The acrylic layer helps to keep the aluminum from damage, and the CD's label is printed on to the acrylic layer as well. Therefore, the layers that make up a CD from top to bottom are the label, acrylic, aluminum, and then polycarbonate plastic. |