DVD Updating, or, DVD Keeping?

We all know, just a few days ago, Toshiba announced they will give up developing, manufacturing and marketing HD-DVD products. After all, the “next-generation format war” ends up. And we also know, Blu-ray Disc and HD-DVD are two new optical storage technologies that were the two sides fighting for the war, that who’s going to be the successor of DVD. Is it really true that DVD has its days tapered off?

DVD is great. It can store movies, music, and even backup data with a DVD burner like Nero. Of course, all the stored can be also conversely ripped out with DVD ripper software like ImTOO DVD Ripper Ultimate. But, with the introduction of high-definition TV (HDTV) to the world, DVD storage capacity showed to be insufficient to this application.

DVD supports a resolution up to 720x480 pixels, while HDTV works with resolutions as high as 1920x1080 pixels. Just to give you an idea, two hours of high-definition video with data compression requires 22 GB of storage space. Keep in mind that the maximum capacity of a DVD is of 17 GB, if a DVD-18 disc is used (a dual-sided dual-layer disc).

So, how to provide a higher data storage capacity for high-definition contents? Here are the two DVD successor candidates: Blu-ray Disc and HD-DVD.

In fact, a Blu-ray Disc or a HD-DVD is just a DVD disc with a higher storage capacity to store high-definition contents. The main motivation to the creation of a DVD successor was the introduction of HDTV, which requires a higher disc storage capacity, features a regular DVD cannot provide. But how a Blu-ray Disc or a HD-DVD is able to store more data than a regular DVD disc?

Both Blu-ray and HD-DVD discs have the same physical size of DVD discs (and CDs), with a diameter of 12 cm (120 mm, around 4 ¾”).

The key to both Blu-ray and HD-DVD technologies is the use of a blue-purple laser to read and write data from the disc. This laser has a smaller wavelength with higher recording density compared to the red laser used by DVD players.

During the recording of a Blu-ray or HD-DVD disc a high-power blue-purple laser is used to burn pits on the disc surface. The areas that weren’t burned are known as lands.

During the reading of a Blue-Ray or HD-DVD disc a blue-purple laser with lower intensity is thrown on the disc surface. When the light reaches a pit it is reflected back with a lower intensity compared when it hit a land. As the pit height corresponds to ¼ of the laser wavelength, the reflected light reaches the photosensor found on the Blu-ray or HD-DVD player half wavelength dephased (¼ on its way in + ¼ on its way back = ½). This is how the Blu-ray or HD-DVD player can recognize if an area is a pit or a land: the amount of light reflected by a land is higher than the amount reflected by a pit.

You could think that each spot where the light is reflected with a higher intensity (land) equals to a “1” bit while each spot where the light is reflected with a lower intensity (pit) equals to a “0” bit. However Blu-ray and HD-DVD players use the transition between pits and lands or lands and pits to represent a “1” bit and the absence of such transitions to represent a “0” bit.

Each bit read this way is called an optical bit. They still do not represent directly a data “0” or “1”. A process known as modulation is still required to convert optical bits into data bits. HD-DVD uses a modulation technique called ETM (Eight to Twelve Modulation), which converts each group of eight data bits (one byte) into 12 optical bits. Blue-Ray uses a modulation technique called 17PP that converts a variable number of optical bits in data bits based on rules defined by the modulation algorithm.

Just like what happens on CDs and DVDs, on Blu-ray and HD-DVD discs pits and lands are organized into a single spiral track that starts at the center of the disc and ends at the border of the disc. The smaller the distance between the spiral tracks, more data can be stored on the disc. On Blu-ray discs this distance is smaller than on HD-DVD discs (0.32 µm vs. 0.40 µm, respectively).

Also, on Blu-ray discs each pit measures 0.13 µm, while on HD-DVD discs they measure 0.20 µm.
But why do HD-DVD discs use bigger pits compared to Blu-ray if both use a laser with the same wavelength? The answer is the distance between the recording layer and the lacquer layer. On Blu-ray discs the recording layer is only 0.1 mm distant from the lacquer layer, which allows a higher recording density (HD-DVD discs use the same distance as DVDs, 0.6 mm). On the other hand Blu-ray discs must be handled more carefully, as any scratch on its surface can easily reach the recording layer, compromising the recorded data. That is why some Blu-ray discs come inside a caddy in order to avoid physical damage.

As we can see, technologically speaking Blu-ray and HD-DVD are very similar, the main difference between the two being the storage capacity.

A single-layer Blu-ray disc can hold up to 25 GB, while a single-layer HD-DVD disc can hold up to “only” 15 GB. A dual-layer Blu-ray disc can store up to 54 GB, while a dual-layer HD-DVD can store only up to 30 GB.
As we saw, on the storage size Blu-ray has a better advantage over HD-DVD, even though Blu-ray discs are more expensive. A single-layer Blu-ray Disc can hold up to 25 GB while the same disc using HD-DVD technology can store only 15 GB. A dual-layer Blu-ray Disc can store up to 54 GB, while the same disc using HD-DVD technology can store only up to 30 GB.

In terms of compatibility, both Blu-ray and HD-DVD players are capable of playing CDs and DVDs, but it won’t be possible to read a Blu-ray disc on a HD-DVD player and vice-versa (it is technically possible to create a player that can read both formats, but it will probably cost almost twice, as it will need two separated circuits inside the unit, one for each technology, and someone are trying to…).

For now, DVD discs continue to be a good choice for the average Joe. If you are not a technology freak, why not just keep going with your Nero and ImTOO?