Recovering data from damaged CDs - possibly with BSD?

dodginess · #1 July 26th, 2005, 08:22 PM

Hi All - this is my first post, so bear with me...

I'm currently trying to get a *big* file off of a CD (in the region of 700MB) but because of some scratches on the disk, all the applications I've tried to use get so far then just give up. Although I've been using Macs for a while there doesn't seem to be any kind of mechanism in applications like Disk Copy to 'retry' reading from the CD, as there (sort of) is with a Wintel machine.

So, does anyone know whether there's any freeware/shareware software that can help me out of this problem? I also figure that there must be another way of retrieving the data through BSD but my knowledge of this is fairly patchy and I don't really know what commands might be applicable - I did try split but didn't get very far

Anyway, any help would be much appreciated!

dodginess

symphonix · #2 July 26th, 2005, 08:49 PM

First of all, if you take the disc to your local video or computer-game rental store, they will be able to run it through a scratch repair machine for a small fee. Do this first.

Being able to read a disc or not is not related to software. If the laser and detection hardware in the drive is unable to determine whether a particular bit is a pit or not due to scratching, then nothing the software can do is going to change that. A different OS is not going to make your drive pick up the data any differently - it simply doesn't have any effect. Your obvious next step, then, is to look at different hardware.

For reading scratched discs, old 4x to 8x speed CD-ROM drives are by far the best. Because they are reading the disc at a slower speed, they're more likely to be able to read the data on a scratched disc.

I used to have an LG-branded 24x drive that I kept lying around, which I dubbed the "Miracle" drive, since it could read extremely damaged discs when nothing else seemed to work. Your best bet is to try the disc in every CD drive you have access to ... friends computers, those old computers rusting away in the top of the wardrobe, and so on. You may well find your own "Miracle" drive.

stringmint · #3 July 26th, 2005, 09:31 PM

I agree with symphonix, but just to clarify why your Wintel machine behaves differently:
an application or OS may alow you to "retry" reading a dud disk, but if it didnt work the first time its highly unlikely to work on further attempts. If a disc is damaged beyond the error tolorance of the drive, repeat attempts wont help.

Ifrit · #4 July 27th, 2005, 03:03 AM

Quote:

Being able to read a disc or not is not related to software.

I can't agree here, software is able to access informations differently. There is software which copies bitwise and doesn't care if the created copy contains all informations or not. Then there is software which operates on a different more high level layer (most likley using the OS functions) and makes sure that all information it attempts to copy is correct (in order to protect the targets file system).

Example: I scratched my friend's rare game CD (it fell down). Windows couldn't read it, OSX didn't want to copy any data. Unfortunally I didn't had access to a DOS machine. So I installed Virtual PC in OSX, set up a DOS guest OS + Norton Commander, copied the game files over to a folder which virtual PC could access and later made a backup CD with the finder.

dodginess · #5 July 27th, 2005, 07:06 PM

Hi All,

Thanks for the advice so far. The slower-reading-speed idea had occurred to me, and as I have an old 8600/200 lying around I'll give it a try. One of the problems with my eMac (though I guess this may be the case with most Macs) is that it keeps switching between different read-speeds, and by the time it hits the duff area it's up to the top speed and consequently is less likely to be able to read the data at this point.

My thoughts also turned to those manual 'grinding' machines that you can buy to repair CDs but they look a bit severe for my liking.

As to whether different software affects the ability to re-read from a CD, I would have to agree with Ifrit here - from my experiences back in the good old days of MS-DOS there were definitely 'good' and 'bad' disk recovery applications. Funnily enough, Norton probably had the best suite going at the time - how things change! Without degenerating into slander or ranting, every version of Norton I've since used on a Mac has managed to break it in one way or another.

Whilst I take on board stringmint's point about the futility of trying to read a 'dead' area, it would clearly be helpful if the OS at least *tried* to re-read the data (possibly at a slower speed).

On a final note, does anyone know if there is any software that can lock the CD reader to a set speed, or am I asking the impossible?

Many Thanks,

dodginess

(BTW: If anyone would like a spare part from the above-mentioned 8600 please get in contact. The hard drive isn't up to much but everything else should be fine. On that note, I also have a lovely little Quadra 700 lying around looking lonely...)