Difference between revisions of "Files:CRC-verified files"

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'''CRC-verified files''' are files that have been tested on file corruption. If you download a file, then you should always make a CRC check on it (provided that a CRC hash was shipped with the file), to prove that your file is a perfect match for the original file. If the CRC check of a file fails, the file may have been changed or your file has been corrupted by the transfer or was bad to begin with. (It happens more and more for groups to spread crc corrupt files.) As a result, the corrupt file (e.g. videos, zip etc) might not be able to open/play or be of any use at all. If you have a corrupt file, you should either redownload it completely or request a patch for it, via a tool such as [[Zidrav]] or [[QuickPar]].
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{{TOCright}}
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*A '''CRC-verified file''' is a file for which the CRC has been found to be the same as a released 'good CRC'; it is very likely that the file is a good copy.
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*A '''CRC-failed file''' is a file for which the CRC has been found to be ''different'' from a released 'good CRC'; ''it is very likely that the file is corrupt in some way''.
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If you've hashed a file for use it with [[ed2kdump]], and AniDB lists it as 'CRC-verified', you don't need to do any further verification: the file is definitely uncorrupted.
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==About CRC==
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A CRC is a form of file hash: a short representation of a longer file that is likely to change if the file is modified. CRC is a 32-bit hash, which means that the chances of a random corruption not changing the CRC are four million to one against. Many groups release CRC hashes of their released files, so you can make sure you've downloaded them correctly.
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Any change, from a single changed bit to widespread changes throughout the file, will change the CRC. While a single-bit error is often imperceptible, files with major corruption may be unplayable. It is possible to patch a corrupt file to a known-good version using a tool such as [[Zidrav]] or [[QuickPar]].  
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The other hashes AniDB lists (MD5, SHA-1, and ed2k) are ''stronger'' than CRC: the chance of a CRC differing between two files with the same ed2k, SHA-1 or MD5 hash is at least 79 billion billion billion to one. If the MD5, SHA-1, or ed2k hash matches a published 'good hash', then it is very unlikely indeed that the CRC will fail. When AniDB lists a file as CRC-verified, you can use any of the hashes listed to verify the file.
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==External links==
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*[[Wikipedia:Cyclic redundancy check|CRC article on Wikipedia]]
  
 
[[Category:Definitions]]
 
[[Category:Definitions]]

Latest revision as of 18:56, 19 July 2011

  • A CRC-verified file is a file for which the CRC has been found to be the same as a released 'good CRC'; it is very likely that the file is a good copy.
  • A CRC-failed file is a file for which the CRC has been found to be different from a released 'good CRC'; it is very likely that the file is corrupt in some way.

If you've hashed a file for use it with ed2kdump, and AniDB lists it as 'CRC-verified', you don't need to do any further verification: the file is definitely uncorrupted.

About CRC

A CRC is a form of file hash: a short representation of a longer file that is likely to change if the file is modified. CRC is a 32-bit hash, which means that the chances of a random corruption not changing the CRC are four million to one against. Many groups release CRC hashes of their released files, so you can make sure you've downloaded them correctly.

Any change, from a single changed bit to widespread changes throughout the file, will change the CRC. While a single-bit error is often imperceptible, files with major corruption may be unplayable. It is possible to patch a corrupt file to a known-good version using a tool such as Zidrav or QuickPar.

The other hashes AniDB lists (MD5, SHA-1, and ed2k) are stronger than CRC: the chance of a CRC differing between two files with the same ed2k, SHA-1 or MD5 hash is at least 79 billion billion billion to one. If the MD5, SHA-1, or ed2k hash matches a published 'good hash', then it is very unlikely indeed that the CRC will fail. When AniDB lists a file as CRC-verified, you can use any of the hashes listed to verify the file.

External links