For example in Debian Wheezy installation CD there is a Check the CD-ROM(s) integrity menu option in debian-installer main menu. Checking the integrity of CD takes few minutes. How are such tests usually done? By simply reading all the files from CD and in case thee are no read errors from file-system, the CD is valid? Or does it involve some sort of hash calculation and comparison?
How do Linux distributions check the CD/DVD-ROM integrity?
debian;debian installer
Checking from an Ubuntu 14.10 ISO I had here, there is a md5sums.txt file in the root directory of the CD. The file has the MD5 sum of the files.cde56251d6cae5214227d887dee3bab7  ./pics/red-upperleft.png0730e775a72519aaa450a3774fca5f55  ./pics/red-lowerleft.pngcd8aa5e7fa11b1362ef1869ac6b1aa56  ./pics/blue-lowerleft.png92091902d3ca753bb858d4682b3fc26b  ./pics/logo-50.jpg461cbc7ff94fdea8008cab34b611abb8  ./pics/blue-upperright.pngThen the installer can compute the checksums of all the files on the CD and compare them against the contents of this file. Just reading all files from the CD wouldn't catch a corrupted ISO that was burned successfully.