[d332]

This inspired me to read up on the low-level details of CD structure. I'm curious if anybody scanned an entire CD and shared the results, so that we could work with a raw image of disc that contains all its quirks, as opposed to the typical .iso format?

[thristian]

It's really difficult. Unlike floppy disks, where you tell the drive to seek and get back raw magnetic pulses (so you can produce raw flux images), or hard disks where you tell the drive to read an arbitrary sector and get a blob of data (so you can produce sector-level images), the protocol for talking to a CD ROM involves asking for track/sector addresses, which means you have to trust the drive to interpret all the track metadata and error-correction for you - you generally can't just dump the "raw" data and do the interpretation yourself.

That's why the most robust CD image format is the BIN/CUE format. The BIN file contains all the sectors the drive allows us to read, the CUE file contains the disc metadata as interpreted for us by the drive firmware.

There are some drives which support extra "raw read" commands, but they're incredibly rare and consequently in great demand by CD preservation projects like redump.org.

Some people have used the contents of BIN/CUE data to reconstruct what should actually be on the disk, but that's not quite the same thing. Here's a great explanation of the CD structure in all its complexity:

https://github.com/higan-emu/emulation-articles/tree/master/...

[AkBKukU]

Even BIN/CUE is not enough. It cannot store subchannel data like CD+G and is only able to hold a single session which breaks bluebook CDs with audio and data.

We do not currently have a widely supported CD standard for storing data from a CD that can properly hold all data. Aaru [0] is close, but still has to output back to other formats like BIN/CUE to use the contents of the disc.

[0] https://www.aaru.app/#/

[edude03]

Apparently makemkv forum members created some patched firmware that lets you raw read BRs for the sake of extracting metadata that’s intentionally hidden for DRM. Though I’ll have to recheck my understanding since you’re saying you can’t actually raw read disks anyway

[ssl-3]

Audio CDs were never ripped/transferred as ISO files. ISO-9660 is a filesystem that came years later, and Redbook audio CDs simply do not contain files.

If you want to look at the structure of a whole audio CD, then one way is to rip it with a decent tool (perhaps cdrdao or EAC) and generate a bin/cue file pair as an output.

[d332]

But that's not my goal. I'd like to be able to observe every grove, the physical encoding of data, and see if I could implement decoding from scratch. First problem is though that I don't know how to get a microscopic image of the disc.

[sho]

Coming back to this, having read some of the (great!) replies, I'm going to go out on a limb and say that in theory, this sounds possible, and fun, but highly impractical. I'll assume that by "scan" you mean a high end "flatbed scanner" optical scan which would return a 2D bitmap.

It's impractical because the resolution required to retrieve the data "flatbed scanner style" is comically high, perhaps 50k dpi, far beyond the capability of any commercial unit and well into scanning microscope territory. Sure, from my understanding, it looks technically possible. But it would be a very significant and costly project just to assemble the image in the first place. Even if you had that, the resulting file would be hilariously huge (something like 122GB), extremely difficult to work with, and you would be starting from scratch implementing some kind of visual pathfinding helical decoder to painstakingly unravel the linear coil of data the scan just sort of blatted into two dimensions.

It's a cool idea. But it's comically, exponentially harder than just using the equipment as intended to just read the laser returns off the disk directly, into a far, far more easily dealt with format.

I'm adding that CD scan to my list of things I'd like to do if I ever get really rich.