Compact Disc

 

see the CD FAQ at:    http://www.cdrfaq.org/ 

The CD (Compact Disc) is a thin, slightly flexible, hard, plastic disc.  The dimensions are 12 cm (120 mm, or 4.8") in diameter and 1.2 mm thick.  The largest layer forms the substrate - it is made of polycarbonate (plastic).  There are other much thinner layers made of metal, resin (laquer) and plastic.  The metal layers are capable of storing digital information as bits. 

CD's differ from Hard Drives in that they have one, extremely long, spiral track (Hard drives have multiple cylindrical tracks).  Also, instead of reading from the outside to the inside, the track begins in the middle and spirals out to the edges.

Type   

Audio (Min)   

Data (MB)

Standard   

74   

650

Oversize 80*  

80   

700

NOTE:  * anything higher than 80 mins is called an "Overburn" CD
They are available for 83, 90, 99, and 120 mins (if you can find them)

In addition to the main data storage, there are two areas of the CD which are required.  The Lead-In area stores CD structure information (Manufacturer, type, etc), and the Lead-Out area notifies the CD drive that the CD information is ending.

There are two primary uses for traditional CD's - they are used to store either digital audio recordings or computer data. Both of these types of compact disc are read-only, which means that once the data has been recorded onto them, they can only be read, or played.  There are also recordable CD's, that come in two flavors . . .  CD-R (CD-Recordable) and CD-RW (CD ReWriteable).  CD-R's can only be written to once, but are universally compatible with PC CD-ROM and CD-Recordable drives.  CD-RW's can be written to many times, but are not compatible with all CD players - actually, they are readable on virtually all modern drives, but some older drives will have trouble with them.

Audio CD's -  Single vs EP vs Album

An extended play or EP, is the name given to vinyl records or CDs which are too long to be called singles but too short to qualify as albums. Typically an album has eight or more tracks (anywhere between 30-60 minutes), a single has one to three (5-15 minutes), and an EP four to eight (or around 15-30 minutes). Some artists, especially in the days of vinyl, have released full-length albums that could fit the definition of a modern-day EP (Yes' Close to the Edge is nearly 39 minutes long; Prince's Dirty Mind is seconds short of a full half hour.) Conversely, there are EPs that are long enough to be albums (Marilyn Manson's Smells Like Children for example, which is 54 minutes long; Estradasphere's The Silent Elk of Yesterday clocks in at 74 minutes, 54 seconds).

A remix single is not considered an EP unless it also has other songs on it (an EP/single hybrid). The name "extended play" has become something of a misnomer, for though it originally was used for singles that were extended beyond the standard length, it is now more often synonymous with an album that is shorter than usual; indeed, EPs are sometimes referred to as "mini-albums" (see below). For this reason, among others, they are referred to as "EPs", the full name being used much more rarely.

EPs were released in various sizes in different eras. In the 1950s and 1960s, EPs were typically 45 RPM recordings on 7" (18cm) disks, with two songs on each side. By coincidence, the format gained wide popularity with the coming of Elvis Presley, and it is sometimes erroneously stated that the term "EP" derived from his initials. Nevertheless, he practically ruled the Billboard EP charts, hitting the top 10 sixteen different times, six of them going to number 1, the latter staying at the top for an amazing 86 weeks. Through his EPs, Presley earned 6 Gold, 10 Platinum, of which 2 were Multi-Platinum RIAA certifications, representing sales in excess of 16.5 million units, the most ever, by any recording artist, whether solo, or group.