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Is my computer supposed to tell me when it can't read a file on a scratched CD?

R

RPatrick6

Member
Hello,

Last night I copied an 80 MB video file from a CD to my hard drive with windows explorer. When I was viewing the file from my hard drive, it haulted in the middle of playback and said the file was corrupted. I visually checked the CD and saw a scratch over some of the data. I cleaned the CD and then transferred the file again and it worked.

Shouldn't an error message be generated when the CD drive cannot properly read a file ? What stops corrupted files from being written to my hard drive when I install software with thousands of files from a CD ?
 
On an optical disk, the drive is reading pits and lands (or absorptive and reflective) and interpreting them as 1s and 0s. As long as what it is trying to read "looks like" 1s and 0s, the drive is happy and no error message will be generated. You need to have your own way to check for data corruption (good commercial software checks its own data integrity during installion). Karenware.com has at least two free utilities that can generate MD5 hashes on files (Dirprinter and Hasher). One must be responsible for verifying his own data's integrity...

.bh.

Here, have a :beer: !
 
Nope. Your computer will happily stroll along while it believes that the CD is reading valid data. If the software has some fail safe built-in, then maybe it will give you an error message.
 
Hi, The system knows when a file is corrupted, or unreadable when the check sum is incorrect. A check sum is calculated and added to the end of the file when it is written. When read a new check sum is calculated and compared to the old one. If they don't agree there has been a error. The read is attempted several more times and if not successful you will get an error message. Jim
 
There is actually data correction built into CD-ROMs -- but this is not foolproof. If there's too much damage, or the data-correction bits themselves are screwed up, you'll read invalid data.

If it truly cannot read anything from the disk (which can happen if it's scratched up badly enough), it will fail the copy with an error message. But it's possible to read invalid data from a CD/DVD and for your system to report it as correct.
 
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