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RID Revisited, or What Writer Wrote that Disc?

June 5, 2018
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Back many years ago there was a small effort made to have CD recorders stamp discs with the serial number of the writer.  There is some description of this on this blog with the latest such article being from 2015.

Not much has changed with this with most writers still preferring not to implement this.  Something that I did not completely understand before is that for DVDs this is also connected with Optimum Power Calibration, the technique that tunes the laser power by writing to the disc and checking the result.  With CD-R discs basically this must be done every time because there is no information about what writer wrote to the disc in the OPC information.  With DVDs this is different.

In the Recording Management Data (RMD) there is a provision to store information about each writer that writes to a disc and what the OPC parameters were determined to be.  The intent of this is to allow software and hardware to work together to know when writing a disc that this disc has already been written to by this writer so no OPC calibration is needed.  The parameters are there and everything should be fine.  This also assumes the disc receives a timestamp from the authoring software so that this can also be stored with the OPC data.  You see, over time the dye in the disc ages and may require different laser power.  This allows the drive and writing software to determine that the writing previously on this drive was done a long time ago (criteria unknown exactly) and that the OPC calibration should be redone.

There are a number of issues with this.

First off, not a lot of software out there sends the timestamp to the drive when writing to a DVD-type disc.  This basically makes the OPC information dateless and therefore useless – you cannot use the same parameters if you last did the OPC calibration years ago.  Without the writing software sending time stamps for each writing event, there is no point to this.  The OPC has to be redone each time.

Similarly, the drive has to actually update/utilize the RMD data.  It is not clear at all that many DVD writers do this.  It appears from our checking of discs that most DVD writers do not update the RMD information with the drive information.  If the OPC information including drive manufacturer, model and serial number are not recorded on the disc, the OPC information cannot be used even when the same drive is used the same day to write more data to the disc.

What I have noticed that changes things is that multiple Blu-ray drives that I have tested are writing OPC information including the drive manufacturer, model and serial number to the RMD data for DVD discs.  I haven’t checked the results with Blu-ray discs as of yet but it would seem highly likely that the information is going to be present there as well.

What does this mean?  Well, today you can buy a Blu-ray writer (BD-R) for a little more than a DVD writer and it is likely that CD/DVD writers will disappear from the marketplace in favor of BD/CD/DVD writers.  If the trend that I have seen with writers here is in fact correct for all BD/CD/DVD writers, it will mean that most discs have the writer serial number encoded on the disc for Blu-ray and DVD discs.

Where does this leave CD-R and CD-RW?  Well, there has been a number of factors that have prevented widespread use of such information on these discs.  For one thing, very few manufacturers chose to write any identifying information to the disc at all and this information was not clearly tied to OPC and reducing the amount of space needed for OPC calibration.  There is an upper limit as to the number of sessions possible to write to these discs and there is “enough” OPC space for things to be good enough.

Also, when identifying information is written to discs, it appears in a number of different locations depending on the drive manufacturer.  This makes the whole process somewhat useless and has been mentioned before as being present so infrequently that there really isn’t any point to even looking for it.

Today, and into the future, the labelling of discs with what writer wrote to the disc will become more important.  This will allow definitive tracking of discs with the writer manufacturer, model and serial number.  How will this affect users?  Very few users today count on any sort of anominity when it comes to discs they have written.  So this labelling will not cause a lot of problems.  In a few cases, having this information which is not readily displayed will provide proof of ownership in cases where there is a dispute.  Clearly there will be greater insight for forensic examiners into the history of a disc and tie it conclusively to a particular writer and possibly to a computer.

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