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Introduction  

Authors: spath & H3rB3i
Date: March 2005

2005 is here and the companies promoting the next generation storage formats are ready for the last and most important rounds in the 'war", which will probably answer the question: which format will become the next standard for movie and data storage?

HD-DVD and Blu-ray: What are the technologies?

These two formats are heralded as the successor to the current DVD technology. Blu-ray and HD-DVD have both been developed to enable recording, playback and rewriting of high definition video and data. The key to these technologies is the blue-violet laser that is used to write the data to the disc. This blue laser has a much shorter wavelength than the current red laser DVD system, which makes it possible to read and write smaller pits, as a result, these discs can hold up to 15 GB (HD-DVD) and 25 GB (Blu-ray) of data on a single sided single layer 12cm disc.

This additional storage capacity will be essential when HDTV becomes mainstream, in order to allow storage of HD TV shows or movies on an optical disc in the same high quality. You can record about 13 hours of standard TV but only a bit more than 2 hours of uncompressed high definition TV on a 25GB disc.

When we take a closer look at the two competing formats, we can quickly see that the dimensions of the discs and the use of a blue laser are about the only similarities the two formats share.

But before we start to compare the two formats to find out the differences, let us explain some terms we will need to know, to understand how it is possible to store that high amount of data on discs that are looking like conventional CDs or DVDs.

Numerical Aperture (NA)

The numerical aperture of an optical lens is a measure of its ability to gather light and resolve fine specimen detail at a fixed object distance.

Together with the wavelength, this is how the NA or the resolution of an optical system is determined. The NA and the wavelength also define the size of the laser beam; the result of a higher NA and a shorter wavelength is a smaller laser beam.

This allows focusing the beam with much higher precision and a reduction of the Track pitch.

Track Pitch

The data track of an optical disc is a spiral starting from the centre of the disc; the distance (in micro meters) between two rows of the track is the track pitch. It is measured from the centre of the row to the centre of the next row.

When the Track Pitch can be reduced, this means that the distance between the rows is lower and that the resulting track is much longer, thus you can store more data.

 So what are the differences between Blu-ray and HD-DVD?

                   * The format will not be available

Disc Structure

When we take a look to the specifications above, we immediately see that the capacity is a most important difference. Blu-ray offers a significantly higher storage capacity. The reason for this is the disc itself: while HD-DVD uses a similar disc to the DVD (0.6 mm disc with 0.6 mm protective coating), Blu-ray steps away from the DVD norm and uses a 1.1 mm disc with a protective layer of only 0.1 mm. The recording layer is therefore very close to the surface of the disc. The advantage is that the laser has less material to read through, which allows a higher NA, a lower track pitch, a smaller pit length and therefore more storage compared to HD-DVD.

But this proximity of the information layer also means that the BD disc is more vulnerable to accidental scratches. Furthermore, the lens has to be closer to the surface of the disc than any other optical disc before, which increases the risks of the lens accidentally hitting the disc. This seems so serious that the Blu-ray standard specifically mentions these risks and even recommends adding a 'bumper" to the OPU. In practice, these high constraints will require a very high precision of both BD media manufacturing and drive's tilt control.

At first the BD discs were supposed to require a cartridge or a special coating to protect the disc, but later this idea was abandoned. Furthermore, TDK has managed to develop a hard coating that complies with the Blu-ray specifications for the disc, this should make a BD more resistant to damage and fingerprints than a current DVD.

The HD-DVD standard, on the other hand, offers a lower storage capacity, but through its similarity to the current DVD's, again no hard coating is required (since the data layer is equally distant from both sides of the disc, it is naturally more difficult to damage). It is also much easier to make future optical drives backward compatible.

Note that Blu-ray offers 3 different storage capacities corresponding to 3 different pit lengths (23.3, 25 and 27 GB), and even smaller pit lengths could be added in the future as BD equipment will improve. On the other hand, HD-DVD offers a single capacity (15 GB) with a fixed pit length. This is actually not truly the case, because the pit length changes on a given HD-DVD disc: indeed, if the data area uses minimum pit length of 204 µm, the so called System Lead In and System Lead Out areas use a minimum pit length of 408 um. The purpose of these half-density regions is all the more puzzling that these pits are there even larger the ones on a DVD-ROM, which is pretty strange for a blue laser disc. Toshiba hinted that this large pit size had been chosen to guarantee that this region will be readable even when pits are badly defined on the disc.

Data Processing

HD-DVD uses a modulation scheme called ETM (Eight to Twelve Modulation) inspired from CD and DVD methods: each byte of data is converted into twelve bits which satisfy to a RLL(1,10) code (all '1' bits must be separated by at least 1 and at most 10

'O' bits). All these conversion patterns are stored into ETM tables similar to EFM/EFM+ tables. Some additional rules exist to limit the number or RL2 (which have a smaller amplitude, thus are harder to read) and to limit the DSV (Digital Sum value).

On the other hand, Blu-ray uses a brand new modulation mechanism called 17PP (RLL(1,7) with Parity preserve/Prohibit RMTR). 'Parity Preserve' means that the modulated bits have the same parity (even or odd number of '1') as the original data bits. 'Prohibit RMTR' means that special replacement rules exist to limit the number of RL2 (similar to what exists for HD-DVD). Contrary to all previous modulation mechanisms (8 to 14 for CD, 8 to 16 for DVD), with 17PP incoming data is considered as a bit stream, which means that at each step a variable number of data bits is modulated, based on a few simple rules. In the end, the overhead is equal to the one added by ETM (+50%).

When pits become smaller, scratches become more difficult to handle because they corrupt more bits. Therefore, both blue formats had to propose new error correction methods which could handle errors more efficiently, especially burst ones. HD-DVD standard went for the easiest solution, all the data containers (frames, sectors, ECC blocks) and error correction algorithms (orthogonal PI/PO corrections) are reused from the DVD standard. The only difference is that that one HD-DVD ECC block corresponds to two concatenated DVD ECC blocks, i.e. an HD-DVD ECC block is 64kB large with 20 columns of PI parity bytes and 16 rows of PO parity bytes. As a result, the maximum correctable burst error length is 7.1 mm (more than DVD).

A HD-DVD ECC block

Blu-ray uses a new error correction strategy, also based on Reed-Solomon codes, called LDC (Long Distance Code) and BIS (Burst Indication Subcode). The LDC parity bytes are RS (248,216,33) codes operating on data columns. The BIS blocks contain control and addressing information, which are protected by independent RS (62,30,33) codes. These BIS blocks are organised in 3 'picket columns", evenly spaced between user data. The idea of these 'pickets" is as follows, when errors are detected in two consecutive BIS codewords, it is likely that this was caused by a burst error, thus that lots of data bytes between these two columns are bad. This information can then be used as erasure indications to increase the correction capabilities of the LDC codes.  

A Blu-ray ECC block

On top of this, two diagonal interleaving steps (similar to what is used on CDs) further decrease the impact of burst errors on error correction. All in all, the absolute Blu-ray efficiency against burst errors is similar to the one of HD-DVD (slightly over 7 mm).

The pros and cons

 Supporting companies

Blu-ray is approved and promoted by the Blu-ray Disc (BDA) association which currently has more than 100 members around the world, the most important and board directors are: DELL, HP, Hitachi, LG-Electronics, Mitsubishi Electric, Panasonic, Pioneer, Philips, Samsung, Sharp, Sony, TDK, Thomson, 20^th Century Fox, Walt Disney, Texas Instruments, Sun Microsystems, the game giants Electronic Arts, and Vivendi Universal Games.

HD-DVD is endorsed and approved by the DVD Forum, the international association of over 230 consumer electronics, entertainment, software, IT and other related companies around the world. DVD Forum even includes member companies of the Blu-ray association and companies that are backing both of the formats. The format is promoted by the HD-DVD Promotion Group, which currently counts 63 member companies. Some of the most important are: Toshiba, Sanyo, NEC, Paramount Pictures, Universal Pictures, New Line Cinema and the Warner Bros Studios.

So, when we take a look at the supporting companies, then it seems that everything is clear. Blu-ray appears to have an edge because most of the electronic giants are supporting the format. But if the key to acceptance is content, the HD-DVD supporting movie studios represent more than 40 percent of Hollywood's films. The Blu-ray backing entertainment companies are, Sony, 20^th Century Fox (which includes MGM) and Disney-Buena Vista, which amounts to about 35 percent. It's close enough at the moment to say that we will most likely have both in the end.

Another indication that we will have both formats, at least for a while, is the fact that some companies like Thomson Electronics have indicated they intend to support both.

Media production / Production costs

The advantage in this case goes to HD-DVD because of the similarity to the current DVD manufacturing processes. This makes it less expensive to adapt the current production lines for producing HD-DVD's. Memory Tech has created a new production line, which can be adapted to produce HD-DVDs in 5 minutes, and this manufacturing line can make 1 HD-DVD in 2.8 seconds. Since the production of a HD-DVD media requires a higher technical precision and therefore a better quality control, we can also await a better quality of conventional DVD medias.

The production of Blu-ray disc will involve more cost, because the companies will have to add equipment for the cover layer portion and it's not that easy to adapt current lines for BD production. Further, it will take about 4-5 seconds to manufacture one media. This is just slightly slower than for a HD-DVD, but multiply this difference by the millions of discs that will be produced and you can see that this becomes an important issue in the cost per unit.

Of course, one could argue that with future innovations it might be possible to reduce the production time for a single disc Blu-ray disc to match HD-DVD efficiencies. But there is still the burden for re-tooling and it seems that it is not possible to produce DVDs on BD adapted production lines. So the companies must have 2 different production lines when they want to produce DVD and BD discs.

Storage capacity 

This is a definite plus for Blu-ray. The single and dual layer discs will offer much more capacity than HD-DVDs. Some developments regarding multi-layer BD discs show us that a Blu-ray disc can hold 8 layers. This offers a potential to store up to 200 GB of data, considerably greater than the theoretical 60GB of a possible double-sided, dual layer, HD-DVD. Of course, who knows if the end user will see such medias in the near future, but we know that it is technically possible.

On the other hand, we have to add that the high storage capacities that BD offers are not really a must for recording high definition content. This is because of new compression technologies, such as MPEG-4 AVC, which makes it possible to produce high quality content at lower bit rates without a visible loss of quality. With this advanced codec technology, it is possible to store 8 hours of high definition video on a 30GB HD-DVD. For the moment, this is enough to store the movie and all the extras.

Transfer Rate/Recording Speed

Here is another advantage for Blu-ray resulting from the NA/Wavelength combination. Since this combination also affects the data density, Blu-ray requires a much lower rotation speed of the disc to reach the specified transfer rate of 36Mbps. A constant rotation speed of 10.000 RPM, which is the current upper limit for optical drives, will result in 12x BD but only 9x HD-DVD. This means that a HD-DVD must rotate faster to reach the same transfer rates.

Something similar applies to the BD-ROM format, compared to current DVDs, Blu-ray provides a five times higher data rate while only doubling the rotation speed of current DVD-ROMs.

Durability

If TDK's hard coat can live up to it's marketing claims, discs provided with the 0.1 mm coating will be even more resistant against damage then current DVDs. The coating is highly scratch resistant and fingerprints can be wiped off to a point where the disc can be read perfectly. This feature will help Blu-ray take an advantage. The negative point is that the coating makes the BD more expensive.

With the integral 0.6 mm protective layer, special coating on the HD-DVD disc is unnecessary. This seems more than logical, because we all know how to handle DVDs. On the other hand, it would be a nice improvement for HD-DVD.

Backward compatibility

Devices that are fully compatible with current red laser technologies (CD and DVD) will be available for both of the formats. NEC has come forward in the press recently with a half height, hybrid drive that is able to handle all three formats (HD-DVD, DVD and CD). Philips presented a drive capable of reading/writing CD/DVD and Blu-ray at this years CES show in Las Vegas.

Unfortunately, there is a problem with Blu-ray and HD-DVD compatibility. With the currently presented devices, we will not be able to playback content on HD-DVD media with a Blu-ray device and vice versa, be it data or games. But this will become essential for both of the formats, at least until one becomes dominant.

We have not seen any evidence of such a technology at the time of this writing. But let's be optimistic, when there are ways to make devices DVD and CD compatible, then surely it is also possible that we will see drives which can handle all of these formats in the future. Of course, this will happen only on the condition that there is a will to produce such devices.

Hybrid Discs

Here we can find an advantage for Blu-ray, resulting from the new structure of the disc. Since the recording layer for Blu-ray data is only 0.1 mm away from the surface of the disc there is enough space below to integrate a complete 8.5 GB DVD DL disc. JVC has already managed to develop such a single-sided disc by using a for red laser transparent Blu-ray layer.

DVD9/HD-DVD is also possible, but not on a single-sided disc. Cinram, one of the HD-DVD backing companies has developed a hybrid disk with two sides. The first consists of a dual-layer DVD that can store up to 8.4GB of data, while the other side is a HD-DVD capable of storing up to 15GB. Memory-Tech and Toshiba has also developed single-sided hybrid discs that contain a 15GB HD-DVD layer and a 4.7GB DVD layer.

Conclusion 

CeBIT update  

CeBIT update

Strategies

From all the press conferences and the discussions we had at CeBIT,
there's a clear difference in strategies between the two camps. HD-DVD
camp considers its format is mature, and after the last technical details
are sorted out in June, production will start full speed. For instance,
NEC plans to sell its first HD-DVD drive this summer (ROM only),
followed by a drive supporting HD-DVD-R and HD-DVD-RW by the
end of 2005.

On the other hand, Blu-ray camp is still working on the BD format and
fixing some compatibility problems. They consider that the high definition
market will be marginal in 2005, and therefore prefer to take their time to
perfect their products. The target is to obtain a mature and more performant
format for 2006, where HDTV is believed to get a real start with the World Cup.

Two different formats - two different marketing strategies. While the companies
around HD-DVD will start on the market with players first, Blu-ray is focusing
their efforts on the burner devices. This seems to be logical when we consider
that some of Hollywoods most important studios are also main backers of HD-DVD.

Prices

Depending on whom you talk to, the manufacturing cost of BD discs is
between 2 and 4 times the price of HD-DVD discs. However, this takes
into account the initial cost of the new manufacturing machines (which
are needed because of the 0.1 mm technology), and it is expected that
this multiplication factor will decrease with time. Note also that we're
talking here about the manufacturing cost of the discs, which represents
only a few percents of its final retail price.

One of the issues we had with HD-DVD was that the -RW format was
completely different from the -R and -ROM formats (see the article).
It seems the reason for this choice was that HD-DVD camp wanted
to achieve higher performances (storage capacity and access times)
with rewritable media than with the other two formats, thus they borrowed
some technologies from DVD-RAM. According to NEC, these differences
will not cause any extra cost for the customer.
  
Copy Protection

One of the issues we had with both copy-protection mechanisms was
the single player revocation scheme, which allows content distributors to
blacklist a given player model. It turned out that drive manufacturers are
also quite annoyed by the practical implications of this scheme, which
was apparently imposed to them by Holywood Majors. At the moment,
it is still not known if and how this feature will be used.

After the HD-DVD press seminar it was clear that copy protection is
still a key concern for HD content providers. One major obstacle to prevent
HD content piracy is of course PC drives, since data can be copied from
the optical media to the hard drive. The HD-DVD camp is well aware of this
problem and explained that they are currently working with PC manufacturers
to define a new PC architecture which could guarantee the security of HD
content. MemoryTech, a company involved in disc manufacturing , even
explained that they were working on a new copy protection scheme combining
the BCA (Burst Curring Area, the bar code in the center of some discs)
with an internet connection.

We couldn't get any definitive statement from the BD camp whether
they would stick to their own BD-CPS scheme or whether they would
adopt AACS. This is still to be decided as part of the finalization of
the BD format.

Lens developments

Samsung Electronics, a board director of Blu-ray told us of developments
regarding the laser lens. As you may know the writing and reading of BD,
DVD and CD requires an optical unit which contains 2 laser lenses, one
for reading and writing of the red laser technologies and one for reading
and writing of Blu-ray. The companies are now on the way to develop a laser
lens which is capable of red and blue laser technologies. This will make
it possible to manufacture much smaller devices, which is a requirement for
portable player and notebook drives.

Conclusion

Conclusion