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Manufacturer Markings on Optical Media

October 2, 2011

One of the more common questions we get from forensic professionals is about the manufacturer markings on CD and DVD recordable media. There is no documentation available about these and it seems like these markings should be valuable. So prosecutors will often insist that the forensic examiner find out as much as they can about these markings, hoping they will lead to identifying where the disc came from.

Sounds like a good approach, right? After all other things with serial numbers, everything from cameras to pacemakers, can be traced with great effectiveness using these serial numbers. So why not discs?

Number on a DVD

A number in a the mirror band on a DVD

The serial numbers on discs are there for a reason, but it isn’t the sort of reason that either consumers or forensic professionals are interested in. The marking is to identify the batch where the disc was produced, and that is all. The manufacturer can then trace this back with their internal quality control and see if a lot of discs had problems in that batch. This is the reason that the information on the disc isn’t unique but relates only to a batch of discs.

The logical question then is how big is this batch of discs? Well, that depends. There are three things that manufactures generally would segregate batches by, and these are listed in order of increasing quantity:

  1. The stamper used in moulding the disc.
  2. The batch of organic dye used in the recording layer of the disc. This applies only to write-once media.
  3. The glass master used to create all of the stampers.

A stamper is good for anywhere between 10,000 and 100,000 discs. There can be a lot of difference with how much dye is mixed up at a time, but it is a safe bet that it is more than 10,000 discs. Finally the glass master can be used to make around 100 stampers, which can be as many as 10 million discs. With really good quality control you can squeeze out even more, perhaps 100 million discs from a single glass master. This means that there can be as many as 100 million discs with the same identification markings out in the world.

A number on a CD-R

CD-R disc with a number printed in the clamping area of the disc.

The markings are determined by two sources: the manufacturer of the disc, and the person or organization contracting for the discs.

Before we get further into manufacturing of discs, we need to take a small step aside for a moment and understand who is manufacturing discs today. I while back, say circa 1995, there were real powerhouses in the manufacture of CD recordable media. TDK, Mitsumi, and a whole host of other companies that were involved in the manufacturing of CD recorders. Since that time, things have changed quite a bit – today the bulk of discs are made by independent contractors in Southeast Asia and are supplied on contract to the “brands” you see in the office supply stores. TDK, for example, no longer makes any discs, they are 100% contracted out and are made with the markings saying TDK on them.

Another example is Memorex. A long long time ago, like in the 1980s, Memorex was a US-based company that made all sorts of things from magnetic tape to mainframe computers. They had a really good reputation for quality in the magnetic tape field. Towards the end of the ’80s Memorex suffered from a lot of problems, most of them probably created by losing focus and getting involved with all sorts of products. So today the products we see labelled Memorex are actually produced on contract for a Hong Kong holding company named Memorex. Memorex, the holding company, actually manufactures nothing at all. But still, Memorex is a prime supplier of recordable media to the consumer market, with sales in the billions of discs.

It is important to understand that if the organization, say Memorex, does not specify to the manufacturer what the markings on the disc should be the manufacturer is free to mark them in a manner to assist them in tracking quality issues. This also helps the contracting party in that tracking down a bad batch of discs quickly is in everyone’s interest. With the quantity of discs that are being made for a large contracting party it is highly likely that the discs are coming from a number of different manufacturers with potentially different sorts of markings.

This is why if you call up the company who’s name is on the disc and ask them what the markings mean they may not be able to tell you much at all. Verbatim and Imation seem to have different policies with respect to this and actually do specify to their manufacturers what the markings should be, but still they are not unique per disc and the actual discs may be made by multiple manufacturers.

About the markings themselves, if the contracting party (think Memorex here) doesn’t specify what the markings should be, the manufacturer will use their own scheme. This is unlikely to be meaningful to anyone except the manufacturer. Given the number of manufacturers that are usually involved, you are going to have to get a long list of Southeast Asian manufacturers and call them individually for assistance. Aside from the problems of dealing with local language and time zones, the manufacturers generally consider this information to be proprietary and they just aren’t interested in revealing it to anyone, even law enforcement.

Finally, we need to address how many of these discs are produced with identical markings. Your average sale in an office supply store, discount warehouse or other consumer outlet is a spindle of 50 or 100 discs. These packages are made up by either the disc manufacturer or some other packager and could potentially have multiple batches of discs included in a single package. But think for a moment about how many 50 disc spindles can be made from 100,000 discs… yes, that would be 2000 spindles. These would likely be sent to a central distribution warehouse and broken up into smaller bunches, say 100 spindles to each store. A network of 2000 stores (Staples has that many) means they are likely to be bringing in at least 200,000 spindles of discs a month or 10,000,000 individual discs. Easily the entire 10,000,000 discs could have the same marking and another 90,000,000 discs could be out there with the same markings but different branding and sent to different central warehouses.

This means the fact that you are holding a disc with a particular marking on it in Atlanta does not necessarily mean that there is not a disc with the identical marking in a store in Los Angeles.

As I mentioned above, the organization contracting for the discs can specify to the manufacturer what markings there should be on them. With speciality discs, such as those sold for “archival” or “medical” purposes often do have unique serial numbers, but at as much as $50 per disc these are unlikely to be found in the hands of average consumers. Could you get lucky and find a disc with a unique serial number? Maybe. But it is unlikely.

With the realities of modern consumer product distribution, it would be nice if we could trace the manufacture of a disc and find out what store it was sold in. This would make it possible to determine all sorts of things quickly and easily. Unfortunately, that isn’t the case. Discs do not have unique serial numbers and do not lend themselves to be traced in any manner whatsoever.

2 Comments leave one →
  1. October 13, 2011 7:22 am

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  2. August 22, 2018 9:56 pm

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