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A normal compact disk has a size of 700 MB but it only holds data upto 650 MB. What is the other 50 MB utilized for?

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up vote 6 down vote accepted

Not all CD's hold the same amount of data. There were a couple different versions produced that attempted to squeeze a few more megabytes out of the standard. The 650Mb/74min and 700Mb/80min standards are the most common. Check out the table in the wiki within the capacity section.

http://en.wikipedia.org/wiki/CD-ROM

They actually hold a little more information beyond the stated capacity of each size and this extra data space is used for error correction data.

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1Kb = 1024 bytes

1Mb = 1024x1024Kb=1048576Bytes = 1Mb

650Mb = 1024x1024x650 = 681574400 bytes

I think the rest is CRC checksums.

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I think this Wikipedia entry explains it quite well: http://en.wikipedia.org/wiki/Compact_Disc

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