I have 3 copies of a CD-ROM that came with a book, and all of them came cracked.

By the third time, I thought that I could probably recover the information using these 3 different discs and completing the missing bits from one another. It seems that just the beginning of the CD cotains information, maybe a few Megabytes, so I could try to do this.

I know it's extremely difficult to do by hand given the amount of bits, but it could be useful to later automate with electronics, knowing exactly how a CD-ROM looks like microscopically, given that a standard CD/DVD drive doesn't seem to give such a low level access but instead just returns errors.

So, how much magnification is required to see the lands and pits, the tracks, and all of the actual structure that would otherwise be seen by the laser of a CD/DVD drive?

Would 100x would be enough, or would I need something more like 600x or 1000x to see an area that contains 650-700 Megabytes?

Or do you know some way to make a CD/DVD drive return every readable bit as well as indicate the unreadable bits so I can then complete the data, even when the drive doesn't seem to detect a CD?

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    contact the book publisher. There is no realistic way to do what you propose. – Frank Thomas Jan 28 '15 at 20:11
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    Upvoting because the question, although kinda far out, is totally valid. – meatspace Jan 28 '15 at 20:31

A 700 MB CD-ROM will have 360,000 sectors, each of which have 2,352 bytes, each of which have 8 bits. So that's 6,773,760,000 1's and 0's you'll be reading with your microscope. If you can read and record 1 bit per second without error for 12 hours a day, you'll be able to get the data off your disk in about 430 years. A microscope that could discern 500 nanometer wide pits wouldn't be exceptionally hard (below is a picture taken at 100X magnification), so it's your call if you think you would be okay staring at images like that for the next 430 years or if you'd prefer a little more fidelity.

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This is a very bad idea.

First off, you're going to have to replicate each of the lands and pits onto a new CD. Not easy.

Secondly, let's say you are trying to recover just 1MB off of a CD by recording each land and pit you see. If you record per bit, you'll be reading upwards of 8 million bits. Now, let's say you can do 2 bits a second. That would be over 46 days of solid work. No eating, drinking, or sleeping. You spend 46 solid days of your life recording each little bit off of a CD (1111 hours). Recovering a full CD (700 MB) would take over 177.5 years.

Third, data forensics of the sort already exist. As long as the cracks aren't near each other, a system could theoretically recover data from all three drives. It would be expensive and slow, but it would be possible. (NB: Another caveat of this is that all three disks must be the exact same. Literal clones of each other. No changes to any files in any way, shape, or form).

Fourth, you'll most likely be able to contact the book's publisher or just download the resources online. They're everywhere.

To answer your other question, it looks like you can see CD bumps/grooves at 1000x, so you'll probably be able to do data recovery somewhere around 1000x.

Forcing a CD to read "unrecoverable" bytes is not really possible.

pits and lands

The long distance between the land and a pit will be recorded as all zeros, or corrupt weird data. Not going to work.

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    1000x is a bit of a stretch, and right at the limit of optical microscopes. An electron scanning microscope would be needed to be able to "practically" read the pits and lands. – Foosh Jan 28 '15 at 20:30
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    What part of this question is practical? – Kaz Wolfe Jan 28 '15 at 20:31
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    Obtaining an electron scanning microscope is more practical of course... – Foosh Jan 28 '15 at 20:38
  • The CD is from an old 1995 book called "Real-Time Animation Toolkit in C++" by Rex E. Bradford. Probably not easy to find anymore. I bought it 3 times even in "New" condition but they all seem to have been deliberately cracked. I think it could be a good exercise anyway to know more about the technology and comparing the lowest level physical media with an ISO image, etc.. Copying to an ISO file instead would be the way to go, but looking for a more automated process. They are supposed to be prepressed CDs so they should be exact. – alt.126 Jan 30 '15 at 1:27
  • The link appears to be dead. – fixer1234 Mar 13 '17 at 4:34

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