What is a Compact Disc?

Mitch Morgan

Since 1982, consumers have had access to one of the great breakthroughs in media storage technology: a slim, round, and shiny object known as the compact disc (CD). Also known as an optical disk, the 4.724 inch (120 mm) round polycarbonate CD has largely replaced less reliable but similar formats like the cassette tape and vinyl record as a unit for digitally stored audio. Despite its size, one standard compact disc may hold up to 80 minutes of music. It remains the most preferred and popular medium for audio recordings. The CD-ROM, a later version of the same technology, holds up to 700 megabytes (MB) of data and is widely used by individuals and businesses for archiving important documents, photographs, and software.

Cassette tapes preceded compact discs.
Cassette tapes preceded compact discs.

A compact disc is a made of a combination of polycarbonate plastic and a reflective layer of aluminum, gold, or other metal. It was modeled after the Laserdisc (LD), a now-obsolete medium that resembles a vinyl record in its size and a CD in its composition. Information is “burned” onto a CD’s metallic layer with a laser, in a spiral direction from the inner part of the CD to the outer rim. This encoded data or audio may then be accessed with optical disc drives like CD players, DVD players, and DVD recorders. Due to the low manufacturing quality of many compact discs, the coated surface or label of a CD may become scratched or soiled to the extent that information becomes irretrievable; however, in most cases a compact disc may be wiped delicately with a lint-free cloth to remove any excess dirt and resolve playback issues.

A stack of CDs.
A stack of CDs.

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Other formats of the compact disc serve many purposes. The mini CD, which is much smaller at 2.362 inches (60 mm) to 3.149 inches (80 mm), holds 24 minutes of audio and is often used by musicians for music singles. The re-writable CD (CD-RW), has the ability to store media and then be “re-written” or replaced with other data at a later date. The CD-R, A similar but non-reusable version, may have information written on the CD only once.

Another version of the compact disc is the Super Audio CD (SACD), which provides high-resolution, surround sound audio a regular audio CD cannot support. A Super Video CD (SVCD) is a lower-quality alternative to a recordable DVD and is used for recording video at a lower bit rate than the standard DVD. Though many alternatives exist, the CD-R remains the most popular version of compact disc for its ability to contain many forms of information and music.

The CD-ROM is an updated version of the CD that's used for documents, photographs, and computer software.
The CD-ROM is an updated version of the CD that's used for documents, photographs, and computer software.

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Discussion Comments


I back up onto memory sticks. That seems to be safer than CDs which seem to stop working, or which can crack.


@zeak4hands - That sounds dangerous. Whenever a CD of mine gets cracked, I give it to my friend. He can repair it if the crack isn't too big -- but if he can't, he adds it to his wall. About half of his room above his computer desk is layered in CD ROMs. He's planning on doing the whole room that way.

They make a really shiny wall. He hangs crystals in his window so that they reflect off of the CDs. It's kind of a weird hobby, but at least it keeps the CDs out of the landfills.


@minthybear19 - I keep lots of backups. Probably too many, but I have a lot to lose. Lots of work related files and music.

The only problem I've ever had with a CD ROM is when I put a cracked one into my computer. It spun for a minute, gaining speed -- then it shattered. It's a good thing I had a cover on my CD ROM drive because the pieces shot all over inside the computer. It was a huge mess and expensive to replace.


@MedicineBall - I actually had the opposite happen. I backed up all of my data onto CDs and not onto my hard drive -- then the CDs I burnt stopped working. I'm not even sure why, but everything on them is corrupted.

I assume that it's from some kind of virus or because my CD ROM burner is so old, but it was very disheartening to lose so much stuff. From now on, I'm keeping a copy on CD and on my back up drive -- just to be safe.


I love CDs. I have a back up hard drive to store all of my data on, but my friend's recently crashed so I backed everything up on CD.

I write a lot of short stories, so I have folders and folders of writing files. I really didn't want to lose them if my back up drive crashed -- since it's getting to be two years old now.

I haven't used CDs in years, so I bought a huge case of them expecting to have to use them all. I forgot how much you can save on a CD. I only ended up using a fourth of the case, so I have lots for later back ups.

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