CD/DVD recording 'area' and custom DVD players

[Kartman]

Hello All,

I know that a typical, standard-size CD (Compact Disc) or DVD (Digital Video Disc) is 12 centimeters (120-mm or 4-11.6/16") in diameter, but I was wondering what the typical 'r' and 'R' are that define the 'inner' (r) radius and 'outer' (R) radius is on these discs for recording. I know the manufacturering methods differ greatly from how CD/DVD+-R/RW are handled, but I just trying to determine the recording area.

I know that some DVDs are two-sided, but I believe (incorrectly?) that no more than 2-layers (per side?) are available for DVDs. I know that some CD burners support over-burning of standard 80-minute CDs to 99-minutes, which implies burining of areas in an area typically not suppose to be used, but available for use in an unadvertised and unsopported case. I'll assume that this 'could' also apply to recordable DVDs, too, but its a little too early in the recordable/re-wrtieable DVD arena to say for certain.

Also, I wonder how difficult it would be for a company like Philips, Lite-On, LG, Sony, etc. to manufacture a DVD drive (player/recorder) based on a disc of a larger diameter. A DVD in the neighborhood of 8-10 inches (20-25 centimeters or 200-250mm) using the same optical transport system currently found in today's DVD-ROMs, DVD players, and DVD+-R/RW units. I would imagine this to be similar to the former LaserDisc players, which were analog devices, but a digital form of LaserDisc might hold the interim solution to providing enough storage capacity for HD (high-definition) DVD material (i.e. movies) at 14.1 and 28.2 Mbps (Megabits-per-second) bit-rates.

As I see JVC pushing the Hollywood studios (four of them thus far) into accepting D-VHS as the only near-term solution to HD pre-recorded materials (movies), I cannot help but think that some would find the introduction of a large-format DVD disc more acceptable than going back to VHS tape (albeit digital). Considering the shelf-life of tape in repeated-use environment, lack of backwards compatability [of D-VHS] to traditional DVDs, etc., I'd venture this would be an entertaining business venture.

What do you think?

 

[zetter]

People are starting do do this already, but not with larger media (noone wants that), but with "blue laser" technology instead of the current red ones. Do a Google for more info.

 

[Kartman]

It is true that several companies (Matsushitsu Corp., Constellation 3D, and InPhase Tech.) are working on 12-centimeter disc storage solutions that would have capacities in the 100Gb region, but all three companies admit they are more than 2-3 years away from from a presence in the marketplace.

Also, the DVD Forum also agreed to a specification to allow MPEG-4 to be used on 12cm discs for HD material, but is has NOT been proved that the additional compression of MPEG-4 offers any benefit whatsoever over MPEG-2 for high definition material, and may actually offer additional problems, introduce unplanned artifacts, etc.

The idea of taking an existing technology and increasing the 'platter' to a larger radius should be rather trivial as the engineering has already been done in 12cm DVD/CD and also in Laser Discs. Thus, a rapidly deployable solution alternate to D-VHS, asy D-LD or LD-DVD, would be of fair consideration. Warping issues with larger discs were easily overcome in the engineering of LDs by the increased disc thickness.

Also, a larger-sized DVD player would be 100% backwards compatible with current DVDs and CDs, which is not the case for D-VHS, but would be of a more immediate solution than Blue-Ray, FMD, or Holographic DVD solutions by the aforementioned commpanies that are planning (2)3-5 year expectations to marketplace.

 

[EmMayEx]

Kartman,

I thought the old laser disc technology was digital but I can't find any handy references.

I agree that it would probably be trivial to design a large format CDR or DVD-R and simply increase capacity by increasing the area as opposed to the areal denisty. A 16.25 cm (6.5") disc would provide twice the capacity (assuming the spindle area is 5 cm in diameter) while a 4X capacity increase would only require a 22.5cm or 8.8" disc. Unfortunately the real problem isn't technology it's what has been established as a convenient standard. I think this helps explain why despite attractive alternatives, some of which are backwards compatible, the 1.44 Mb floppy is still with us today while the 5 1/4" drives are all but extinct.

There might be some market for a large format CDR or DVD-R but there already are a range of optical, magneto optical, and magnetic devices that serve this niche market so I expect competition there would be tough. You would have the advantage that your large format device would support CD's CDRs CDRW's DVDs etc but you run into the problem of serving two different and unrelated markets. I don't think you'd manage to break into the consumer market in any significant way given the HUGE base of installed CD and DVD players and the ubiquity of the 5 1/4" format even if you were 100% backwards compatible.

I also think the music and movie industry are actively fighting the introduction of any new consumer digital recording technology, especially if it offers increased capacity.

I think you are right that the current state of the art DVD systems available for consumer use max out at a dual sided dual layer capacity of 17GB but these should be able to accomodate most HDTV offerings, albeit with fewer extra features and possibly at lower quality due to higher compression. My expectation is that HD Video will not be widely adopted over the next 2-3 years and that this will allow storage technology to catch up.

So from a technical standpoint I see no issue with your idea, but I see considerable market risk on the business side which couuld explain why nobody offers this technology.

Max L.

 

[CTho9305]

one issue with "really big" disks is rotational speed. if you watch an audio CD playing, it slows down as you get to outer tracks to keep the linear velocity the same. However, a data CD (in modern drives, at least) spins at a constant speed so that the outermost part reads at, say, 52x, but the inside is moving at a lower linear velocity, so you get, say, 12x (wild guess).

A recent experiment showed that if the inside of a modern CD is moving such that it can be read at about 50X, the cd will explode or otherise deform itself because of the "centrifugal forces". (if you look around slashdot you might find the article)

A very large disk would have a much greater difference in speed from the outside to the inside. Also because of its larger size, you would not be able to spin it as fast (larger radius = even more centrifugal force), so the inside of the disk would be very very slow to read.

And, of course, current drive bays are 3.5" and 5.25". If your media are bigger than that, it raises a lot of other issues.

 

[Sahakiel]

Heh. I have an idea. Let's RAID DVD's...

 

[bizmark]

I thought the old laser disc technology was digital but I can't find any handy references.

This all comes from vague memories, and I'm sure it's oversimplified, but I think it's correct. Please correct me if I'm wrong.

LaserDiscs are digital in the same sense that CD's are digital. Any video source has an analog waveform; e.g. that which comes over cable lines. It's just a simple waveform: amplitude varying over time. The 1's and 0's on a laserdisc simply mimic this waveform in the same way that a CD mimics the audio signal. (I doubt that it was as straightforward as CD's encoding, but there was a direct algorithm for going for one to the other.)

DVD's encode the data through compression such that the waveform is not obtainable directly. DVDs must be decoded, and the varying quality of decoding chips can result in artifacts or other problems with DVDs. As an illustration, 20 seconds of a black screen on a LaserDisc would take up the same amount of space as 20 seconds of a complex battle scene. A DVD, on the other hand, would require much more physical storage space for the complex battle scene than the plain blank screen. There are many resources available where you can find out about the MPEG coding that's done in DVD's.

 

[Kartman]

Originally posted by: CTho9305
one issue with "really big" disks is rotational speed. if you watch an audio CD playing, it slows down as you get to outer tracks to keep the linear velocity the same. However, a data CD (in modern drives, at least) spins at a constant speed so that the outermost part reads at, say, 52x, but the inside is moving at a lower linear velocity, so you get, say, 12x (wild guess).
A recent experiment showed that if the inside of a modern CD is moving such that it can be read at about 50X, the cd will explode or otherise deform itself because of the "centrifugal forces". (if you look around slashdot you might find the article)
A very large disk would have a much greater difference in speed from the outside to the inside. Also because of its larger size, you would not be able to spin it as fast (larger radius = even more centrifugal force), so the inside of the disk would be very very slow to read.
And, of course, current drive bays are 3.5" and 5.25". If your media are bigger than that, it raises a lot of other issues.

CTho9305, thanks for ther reply! I would be interested in learning the rotational speed of laser discs, and an extrapolation of the max/min data throughput as a function of this rotation speed to insure that a 28.2Mbps high-def data stream is not 'underrun'. Also, keep in mind that the suggestion was not for data customers, but consumer electronics. Thus, the 3.5/5.25" bay limitation need not apply, and even if it were used for data customer applications an external firewire/USB2 should do sufficiently for external portability (much like JVC's D-VHS).

 

[Kartman]

I would be first to say that I honestly do not know if laser discs (LDs) are/were digital or not. Even if they are/were they certainly weren't advertised as such, which brings to opportunity the marketing aspect. Maybe another email to the editor of WideScreen Review is in order!?!

 

[Kartman]

EmMayEx, thanks for the reply. Yes, it would seem that its more politics than technical limitations. I would not doubt the studios would not want to place into the hands HD content on media with a long shelf-life and high-wear resistent form. One could do a lot of bootlegging from this, including down-sampling to bootleg lower DVD-quality copies.