It is a calculation made from all the data in a file to insure accuracy in transmission. When you add a file to a Zip file, WinZip calculates a CRC value for the file and saves the value in the Zip file. When you later extract the file from the Zip file, WinZip calculates the CRC of the extracted file and compares it to the value stored when the file was zipped. If these two CRC values do not match, the file that was extracted does not match the original file, and WinZip will display a CRC Error message. When the data in a Zip file is damaged, it may not be possible to extract all of the files from the Zip file correctly.
Damaged data can affect the entire Zip file, multiple files, or just one file.
Why CRC Errors Occur There are many possible causes for data damage. Among the most common is telephone line noise or some other transfer error when downloading a Zip file from an online source such as the Internet, AOL, or CompuServe. Such an error can introduce invalid data into a Zip file. Some other possible causes include exposure of disks to excessive temperatures or magnetic fields, cross-linked disk sectors, and mechanical problems with disk drives. What to do if a CRC Error Occurs The best solution to the problem of a damaged Zip file is to try to obtain another copy of the file.