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Total no of sectors on CD don't makeup total capacity of CD.

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(@yunus)
Posts: 178
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Topic starter
 

Hello,

We have a CD -with only 10 MB of content- which we wanted to look at all the sectors just like we do in hard drives. So, if you have a hard drive of 500 GB, and if you look at the sectors (in disk view in Encase) you can see all sectors, and you can go until the last sector, and if you multiply the total of number of sectors with 512 byte, it makes a total of 500 GB in the end, which is right.

I would normally expect this to be valid for the CD-Rs except for the sector size being 2048 byte. However, when I looked at the CD "In disk view in Encase", I can see the sectors, however the sectors come to an end not at 700 MB, but where the content ends (at 10 MB). I mean, normally, I would expect to be able to browse the sectors -like in a hard drive - until I see 700 MB of area, but I can not, because the last sector finishes at the 10 MB point, not at 700 MB where the CD capacity is.

Why do you think this happens? Is it because the sectors of a CD-R are created when the CD is burned (unlike a hard drive), so the unburned areas of the CD do not show up in Encase disk view, so in this case, an area of 10 MB on the CD is burned and that is why I can see an area of 10 MB, not full area of the CD.

Regards,

 
Posted : 13/06/2016 10:16 pm
jaclaz
(@jaclaz)
Posts: 5133
Illustrious Member
 

Why do you think this happens? Is it because the sectors of a CD-R are created when the CD is burned (unlike a hard drive), so the unburned areas of the CD do not show up in Encase disk view, so in this case, an area of 10 MB on the CD is burned and that is why I can see an area of 10 MB, not full area of the CD.

Sure.
If you keep the disc at the right angle under a concentrated light you can actually see which part is actually "burned".
http//www.sciencebuddies.org/science-fair-projects/project_ideas/CompSci_p017.shtml#summary

jaclaz

 
Posted : 13/06/2016 10:42 pm
JaredDM
(@jareddm)
Posts: 118
Estimable Member
 

Because most CDs are a write once technology, they aren't preformatted with zero'ed out sectors like a HDD is. The data is actually written in tracks, not technically sectors, though it's translated back to the system like sectors. So what you're seeing is actually very normal.

 
Posted : 13/06/2016 11:30 pm
(@sgreene2991)
Posts: 77
Trusted Member
 

Sure.
If you keep the disc at the right angle under a concentrated light you can actually see which part is actually "burned".
http//www.sciencebuddies.org/science-fair-projects/project_ideas/CompSci_p017.shtml#summary

jaclaz

That was so unhelpful I don't even know where to begin…

But JaredDM is right, since CDs aren't preformatted you are unlikely to find "sectors" per se. With that being said I have seen CDRWs that have a sort of "sector like" pattern to them that filled the disk, but that was an anomaly in my experience.

 
Posted : 14/06/2016 2:32 am
jaclaz
(@jaclaz)
Posts: 5133
Illustrious Member
 

That was so unhelpful I don't even know where to begin…

Why unhelpful? ?
Yunus already answered correctly to his own question

… so in this case, an area of 10 MB on the CD is burned and that is why I can see an area of 10 MB, not full area of the CD.

and I just confirmed how a "burned" CD is only burned for the amount of sectors (or tracks) that contain the data, and that this can also be confirmed visually.

I am not at all current with Encase, and I have no idea how it would manage multisession CD's [1] or other "strange" formats, I would personally rather use a more "optical media" dedicated tool, like Isobuster or similar, but visually inspecting the actual media is still a good way to understand if it contains 10 or 100 Mb of data.

jaclaz

[1] In the good ol' days it was possible to create a multisession CD without importing "previous session" effectively "hiding" data (the "previous session(s)) to most programs.

 
Posted : 14/06/2016 1:43 pm
(@athulin)
Posts: 1156
Noble Member
 

I would normally expect this to be valid for the CD-Rs except for the sector size being 2048 byte. However, when I looked at the CD "In disk view in Encase", I can see the sectors, however the sectors come to an end not at 700 MB, but where the content ends (at 10 MB). I mean, normally, I would expect to be able to browse the sectors -like in a hard drive - until I see 700 MB of area, but I can not, because the last sector finishes at the 10 MB point, not at 700 MB where the CD capacity is.

Right.

You are confusing total capacity (which is how much data can be theoretically stored on a medium, and which is what is usually printed on the CD label, or appears in brand advertisements), with utilized capacity (which is how much data it actually been written to a particular medium at some given moment).

In order to discover the latter, you need to look at low-level structures, such as table of contents etc. I'm not sure how well EnCase does that – I'd be inclined to double-check with specialized tools like ISObuster or CloneCD that actually know how to talk to a CD reader, and that also may get updates somewhat faster. I recommend ISObuster, but I find CloneCD does a great job of imaging even badly damaged media. (There are others InfinaDyne specializes in the field, for example, and their "CD/DVD Inspector" does provide information about basic medium layout.)

You may want to check Paul Crowley's book "CD and DVD Forensics", even though it is more of a user guide to Infinadyne software (haven't read the new edition, though). I think the important parts (i.e. non-user guide material) were reprinted in "Alternate Data Storage Forensics". Anyway, it makes a good place to start, if you know how to identify and skip unimportant stuff.

For the really nitty gritty details, you need to go to standard texts, such as Red Book (or alternatively IEC 60908), Yellow Book (much of which is also found in in ISO/IEC 10149 or ECMA 130), Orange book (parts of which can be found in ECMA 394 and 395), … and so on and so forth.

It's heavy stuff, though. Some standards are modified by later texts, so you really need to know all in order to be on top of the matter. And some of the original texts may still require non-disclosure agreements before you're allowed to access them.

Kris Kaspersky's book "CD Cracking Uncovered" (out of print) contains much information, and describes much of what those standard texts contain, but can also be difficult to read, as it presupposes a fairly high knowledge of software development.

 
Posted : 15/06/2016 10:29 am
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