Data Capacity of CDs
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Data Capacity of CDs
You can fit on a S/VCD without overburning:
- approx. 735 MB of MPEG data onto a 74min/650MB disc
- approx. 795 MB of MPEG data onto an 80min/700MB disc
You can fit on a CD-ROM without overburning:
- approx. 650 MB of data onto a 74min/650MB disc
- approx. 703 MB of data onto an 80min/700MB disc
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VCD stands for 'Video Compact Disc' and basically it is a CD that contains moving pictures and sound. If you're familiar with regular audio/music CDs, then you will know what a VCD looks like. A VCD has the capacity to hold up to 74/80 minutes on 650MB/700MB CDs respectively of full-motion video along with quality stereo sound. VCDs use a compression standard called MPEG to store the video and audio. A VCD can be played on almost all standalone DVD Players and of course on all computers with a DVD-ROM or CD-ROM drive with the help of a software based decoder / player.
SVCD stands for "Super VideoCD". A SVCD is very similiar to a VCD,it has the capacity to hold about 35-60 minutes on 74/80 min CDs of very good quality full-motion video along with up to 2 stereo audio tracks and also 4 selectable subtitles. A SVCD can be played on many standalone DVD Players and of course on all computers with a DVD-ROM or CD-ROM drive with the help of a software based decoder / player. It is also possible to use menus and chapters, similiar to DVDs, on a SVCD and also simple photo album/slide shows with background audio. The quality of a SVCD is much better than a VCD, especially much more sharpen picture than a VCD because of the higher resolution. But the quality depends how many minutes you choose to store on a CD, less minutes/CD generally means higher quality.
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Introduction
Let us ignore for now the terms of megabyte for CD capacity and try to understand how the data is stored on a CD.
As well all know, the data is stored digitally as binary data. This means, however the actual information is actually kept on the disc, this information is in the form of "1"s and "0"s. Physically, the information on a CD is as pits on a thin sheet of metal (aluminium).
An a CD-R disc, the data is physically on an organic dye layer which simulates the metal layer on a real pressed CD.
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How is the information structured
Now, on the CD, the information isn't just organised from beginning to end willy-nilly. Otherwise, it would be really hard to find a useful piece of information on the CD.
Rather, the information is organised in sectors. Consider a sector as like a page in a book. Just like you are able to quickly find something in a book if you know the page number, you can quickly find something on a CD if you know the sector number.
Now, remember that the CD was original made to hold audio data. It was decided, that the CD would would 75 sectors per second of audio. Although I cannot guess where this number comes from, it is quite appropriate for the audio CD. It means that you can "seek" an audio CD accurately to 1/75th of a second -- which is more than enough for consumer purposes.
Now, with this in mind, we can work out the total data capacity of user data for 1 sector.
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The total data capacity of user data of 1 sector on a CD
CD audio uses uncompressed PCM stereo audio, 16-bit resolution sampled at 44.1 kHz.
Thus 1 second of audio contains:
16 bits/channel * 2 channels * 44100 samples/second * 1 second
= 1411200 bits
= 176400 bytes
Since there are 75 sectors per second
1 sector
= 176400 bytes / 75
= 2352 bytes
One sector on a CD contains 2352 bytes max.
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The concept of different MODES and FORMS of burning
Now, audio CD was well and good, but the medium would become much more useful if you could store other data on the disc as well. This became to be know as CD-ROM of course.
Now, the audio-CD uses the ENTIRE sector for audio data.
