Why is a CD 700mb?

Answer 1

Because this is how much they could safely squeeze onto a standard sized CD. A normal CD is actually only 650Mb as this is how much space was required to hold 74 minutes of uncompressed PCM audio. 74 minutes was chosen as this is the length of Beethoven's 9th Symphony.
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note to JTTech .. Giga is Billion, not Trillion. That's Tera.
note to others, they do make 800Mb CD-R's but you won't see too many of them as they're not compatible with nearly as many drives as 700Mb ones are. There are also 900Mb/100 minute CD-R's as well. You will never see a major manufacturer put these on your corner store's shelves.

Answer 2

Hello,

CD stands for compact disk. 700MB Is the capacity that the CD can hold in this case 700 million bytes. Mega (M) is a million. Giga (G) is a trillion. That is the maxium capacity for the CDFS format.

Answer 3

Because that is all the data the CD surface will hold for that format. 700MB. They used to be 650MB but they decided the outer ring could hold some data.

Answer 4

There are artistic, commercial, and technological factors that combine to explain "why."

The original target storage capacity for a CD was one hour of audio content, and a disc diameter of 11.5 cm was sufficient. However, according to Philips, Sony vice-president Norio Ohga suggested extending the capacity to 74 minutes to accommodate a complete performance of Beethoven's 9th Symphony on a single disk [4]. The extra playing time required changing to a 12 cm disc.

According to a Sunday Tribune interview [5] the story is slightly more involved. At that time (1979) Philips owned Polygram, one of the world's largest distributors of music. Polygram had set up a large experimental CD disc plant in Hanover, Germany, which could produce huge amounts of CDs having, of course, a diameter of 11.5cm. Sony did not yet have such a facility. If Sony had agreed on the 11.5cm disc, Philips would have had a significant competitive edge in the market. Sony was aware of that, did not like it, and something had to be done. The long-playing time of Beethoven's Ninth imposed by Ohga was used to push Philips to accept 12cm, so that Philips' Polygram lost its edge on disc fabrication.

The 74-minute playing time of a CD, being more than that of most long-playing vinyl albums, was often used to the format's advantage during the early years when CDs and LPs vied for commercial sales. CDs would often be released with one or more bonus tracks, enticing consumers to buy the CD for the extra material. However, attempts to combine double LPs onto one CD occasionally resulted in an opposing situation in which the CD would actually offer fewer tracks than the LP equivalent.

The main parameters of the CD (taken from the September 1983 issue of the compact disc specification) are as follows:

Scanning velocity: 1.2–1.4 m/s (constant linear velocity) - Equivalent to about 500 rpm at the inside of the disc, or about 200 rpm at the outside edge.
Track pitch: 1.6 μm.
Disc diameter 120 mm.
Disc thickness: 1.2 mm.
Inner radius program area: 25 mm.
Outer radius program area: 58 mm.
The program area is 86.05 cm², so that the length of the recordable spiral is 86.05/1.6 = 5.38 km. With a scanning speed of 1.2 m/s, the playing time is 74 minutes, or around 650 MB of data on a CD-ROM. If the disc diameter were 115 mm, the maximum playing time would have been 68 minutes, i.e., six minutes less. A disc with data appearing slightly more densely is allowable. Using a linear velocity of 1.2 m/s and a track pitch of 1.5 micrometre leads to a playing time of 80 minutes, or a capacity of 700 MB. This is the limit for most conventional audio CDs today.

Another technique to increase the capacity of a disc is store data in the lead out groove that is normally used to indicate the end of a disk, and an extra minute or two of recording is often possible. However, these discs can cause problems in playback when the end of the disc is reached.

CD capacities are always given in binary units. A "700 MB" (or "80 minute") CD has a nominal capacity of about 700 MiB, but DVD capacities are given in decimal units. A "4.7 GB" DVD has a nominal capacity of about 4,489 MiB.

Answer 5

Space restrictions due to the writing method.

Answer 6

it is simply the maximum space they could create in that formatting type

Answer 7

just coz ... they make 800mb cds to ya know ....