Compact disc

Compact disc (CD) is a digital optical disc data storage format. The format was originally developed to store and play only sound recordings but was later adapted for storage of data (CD-ROM). Several other formats were further derived from these, including write-once audio and data storage (CD-R), rewritable media (CD-RW), Video Compact Disc (VCD), Super Video Compact Disc (SVCD), Photo CD, PictureCD, CD-i, and Enhanced Music CD. Audio CDs and audio CD players have been commercially available since October 1982.

Standard CDs have a diameter of 120 millimetres (4.7 in) and can hold up to about 80 minutes of uncompressed audio or about 700 MiB of data. The Mini CD has various diameters ranging from 60 to 80 millimetres (2.4 to 3.1 in); they are sometimes used for CD singles, storing up to 24 minutes of audio, or delivering device drivers.

At the time of the technology's introduction in 1982, a CD had greater storage capacity than a personal computer hard drive. By 2010 hard drives commonly had capacities exceeding those of CDs by a factor of several thousand.

Compact

Compact as used in politics may refer broadly to a pact or treaty; in more specific cases it may refer to:

Mathematics

Disc

Disc or disk (computing and American English) may refer to:

Data storage

The Compact

USA

The Compact is a social and environmental movement whose members promise not to buy anything new for a year. It was started in San Francisco. The movement began as a challenge among 10 friends in 2006.

Goals of the Compact:

Members of the Compact are only allowed to buy underwear, food, and health and safety items such as brake fluid and toilet paper. During their one year vow the Compact members must shop only at second hand stores. They can also barter or simply share with each other for goods they want. One's trash is another's treasure. Compacters use Freecycle.org or freegle http://www.ilovefreegle.org/ where they post what they want and what they are giving away so that they can avoid buying new and still get the goods they want. Craigslist.org is another source of used goods. Many people following the Compact also join a Yahoo! Group for continued conversation and support.

Optical disc

In computing and optical disc recording technologies, an optical disc (OD) is a flat, usually circular disc which encodes binary data (bits) in the form of pits (binary value of 0 or off, due to lack of reflection when read) and lands (binary value of 1 or on, due to a reflection when read) on a special material (often aluminium ) on one of its flat surfaces. The encoding material sits atop a thicker substrate (usually polycarbonate) which makes up the bulk of the disc and forms a dust defocusing layer. The encoding pattern follows a continuous, spiral path covering the entire disc surface and extending from the innermost track to the outermost track. The data is stored on the disc with a laser or stamping machine, and can be accessed when the data path is illuminated with a laser diode in an optical disc drive which spins the disc at speeds of about 200 to 4,000 RPM or more, depending on the drive type, disc format, and the distance of the read head from the center of the disc (inner tracks are read at a higher disc speed). Most optical discs exhibit a characteristic iridescence as a result of the diffraction grating formed by its grooves. This side of the disc contains the actual data and is typically coated with a transparent material, usually lacquer. The reverse side of an optical disc usually has a printed label, sometimes made of paper but often printed or stamped onto the disc itself. Unlike the 3½-inch floppy disk, most optical discs do not have an integrated protective casing and are therefore susceptible to data transfer problems due to scratches, fingerprints, and other environmental problems.