DVD minus has an additional ring, DVD plus not

Look accurately at the inner data edge of the DVD minus.
The data does not start at the completely inner edge, but there is a gap. And then, there is an additional ring that only DVD minus has.
The footprint of that ring is also visible on the label side too.

What significant meaning does that ring have?

It contains the pre-written data; originally there for implementing CSS copy protection. It also contains information such as the MID and recommended write strategy,

It is written after manufacture using a specially modified drive and specific software (see sample screen shots):



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More details?

Where does DVD+R(W) store the MID?

Does DVD-R for authoring also have that ring?

Just seen the edit.

DVD+R stores this information in the stamped ADIP (pregroove).

For the authoring format - no idea - but my guess is “no”.

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IIRC from ecma 267, there is a “control data” zone consisting of 192 repeated copies of the same ecc block (ie. 16 sectors per ecc block) repeated from sector id 0x2F200 to 0x2FDFF. (Sector id 0x30000 is LBA 0). This control zone is not directly accessible by generic scsi read commands.

In one of these 16 sector ecc blocks in the “control data” zone on dvd-video discs, somewhere in the 3rd to 16th sector contains the CSS disc keys. The 1st and 2nd sectors have “physical format information” and “disc manufacturing information”. Without going into details, some of this information is indirectly accessible by a few scsi commands specific to dvd discs.

My guess is the reason for making this “control zone” non-writeable, is such that it prevents easy bit-for-bit copies of dvd-video movie discs, where the CSS disc keys cannot be replicated exactly in the “control zone”. So garden variety dvd copiers will have to remove the title key encryption by hand, which is frequently a dead giveaway that a movie disc might be a pirated copy. Just about all the big movie companies will have a minimum of generic CSS encryption on their movie dvd discs, even if it is just “going through the motions”.

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How do you know it so well?

In the case of the “control data” zone stuff, some of it is documented in the ecma 267 document.

The parts I’m not as certain about, was from looking at the libdvdcss library code and running some of the functions to see what kind of data it dumps out. Mostly guesswork.

At this point I don’t know of any easy ways to directly access sectors id 0x2F200 to 0x2FDFF

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Some information about the control data zone is also covered in the scsi mmc documents.

The scsi “read dvd structure” (0xAD) command can indirectly read some of this data.

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