Although the disc storage technology began with CD, it was the advent of DVD in 1997 that made the essential breakthrough in making of discs of high storage capacity. With a typical DVD, you can store a full-length movie in higher resolution format with Dolby sound features as it has six times more storage capacity than a CD.
However, a DVD, even with its 4.7GB storage capacity and its MPEG-2 compression technique, you can only store videos of standard definition but high definition videos and audios which needed discs of still higher capacity than a DVD. This led to the development of HD-DVDs and Blu-ray discs which have one thing in common – they can hold three to five times more data than a DVD.
As for the video & audio format and other features, HD-DVDs and blu-ray discs differ so much from each that that they are truly incompatible storage media formats. Currently, HD-DVD is slowly dying in the home video market as blu-ray disc has overtaken it as better storage medium for high definition videos. Despite the unending popularity of DVDs, blu-ray disc market is expected to grow faster as the newer blu-ray disc players come with compatibility with CDs and DVDs.
How is a blu-ray disc different from other discs?
Whether CD or DVD or blu-ray discs, they are all optical discs (technically speaking) as they use light (laser beam) to read data which are recorded on their surfaces in the form of bits or bumps. Compared with CD, on a DVD, the pit size is minimized and the tracks are much more densely knitted, so, much larger amount data can be written on a DVD. Video compression methods like MPEG-2 and advanced data error correction methods also enable a DVD to increase its data storage capacity.
Blu-ray discs are more advanced optical discs than DVDs and can store much larger information on the same area (12 cm diameter) by further minimizing the pit size and increasing data density on their surfaces. In addition, a blu-ray disc essentially differs from their predecessors in following ways:
- Blu-ray disc uses blue laser instead of red laser which is generally used by DVDs/CDs.
- The shorter wave length of blue laser (405 nm) can read and write much more data on the same area.
- The image sensor in a blu-ray disc player comes with advanced optical features that help the lens to focus the laser on smaller area.
- Newer blu-ray discs come with advanced polymer coating technologies that make them scratch-proof and highly durable.
Data storage capacity of blu-ray discs
Disc capacity of blu-ray depends on whether it is single layered or double layered. A single layer blu-ray disc can store up to 25 GB of data while a double layer disc has up to 50 GB data storage capacity. In comparison, a double layered DVD can store up to 30 GB of information.
As for playback time, a double layer blu-ray can playback standard definition videos for more than 22 hours and high definition videos for five to eight hours.
A new variant of blu-ray disc ‘quad-layer’ that has four layers and 100 GB capacity has already been rolled out by TDK while developments in blu-ray technology to hold 250 GB capacity are currently underway by some of the manufacturers.
Resolution, audio and compatibility features
Standard DVDs come with EDTV resolution (480p) and cannot support higher resolutions. However, blu-ray discs can store video details in high definition format, i.e., 720p or 1080i or 1080p resolution. In addition, they are also compatible with lower DVD resolution so you watch DVDs using a blu-ray disc player.
Blu-ray discs support high definition audio standards like Dolby True High-Definition, DTS, DTS-High Definition Master Audio, Dolby Digital Plus and DTS Uncompressed linear PCM.
Other features
Blu-ray disc players come with higher drive speeds than HD-DVD players. A 6X drive can have data transfer rate at 36 Mbits/s for writing purposes. This is nearly double the speed of a HD-DVD player. Many latest blu-ray disc players have drive speeds up to 54 Mbits/s.
Blu-ray discs are compatible with video standards like VC1 encoding, MPEG-2 and MPEG-2.
With Blu-ray disc, you can connect to VoD services and download videos although you need to make sure that your blu-ray disc player comes with Ethernet ports and other networking hardware.
Although stand-alone blu-ray disc players are available, video game consoles like Playstation 3 can be used to play blu-ray discs.
While numerous movies (more than 50,000) are available in DVD format, you can find less than 1000 titles available in blu-ray disc format. Hundreds of titles are available in HD-DVDs, however, you cannot play a HD-DVD movie on your blu-ray player due to incompatibility issues.
Blu-ray discs come with region codes meaning you can not play a blu-ray disc that is encoded with another region code. However, the regional coding is sometimes optional, depending on the manufacturing.
Currently, blu-ray disc players and discs are very expensive when compared with DVD or HD-DVDs. A blu-ray disc player or blu-ray disc is nearly four times costlier than HD-DVD.
While all Hollywood studios support DVD format, they are divided over the format of HD-DVD and blu-ray. Studios like Universal, Dreamswork Animation and Paramount use HD-DVD while Sony pictures, Miramax, Touchstone and Fox studios use blu-ray as format for their movie releases.
Types of blu-ray discs
While blu-ray disc technology in common, features like size, capacity, data transfer speed, read-write feature, applications and other features may vary that led to different types of blu-ray discs.
Here are some of the types of blu-ray discs:
Low capacity blu-ray discs
As regular blu-ray discs are much expensive, some discs use BD5 and BD9 standards that provide as much capacity as a double layered DVD but contain blu-ray quality video and audio features. These discs are compatible with DVD and blu-ray format and can also be used with home computers.
Mini Blu-ray discs
They are smaller in size (8 cm diameter) and can hold more than 7 GB of data. They come with BD-R and BD-RW features and they are often used in compact camcorders and other such devices.
BD-R and BD-RE discs
Blu-ray disc recordable come with two types of features. With BD-R discs, data can be written only once while BD-RW discs allow data to be erased and recorded as many times as you like. You can find both the features in regular and mini blu-ray discs.
AVCREC discs
It is another lower capacity variant disc for storing data with blu-ray format on a standard DVD disc. This type of discs find applications that need to use cheaper blu-ray discs such as camcorders or production of high definition video contents meant for broadcasting.
Blu-ray/HD-DVD hybrid discs
This type of discs are compatible with both blu-ray and HD-DVD format as data is stored on one side of the disc using blu-ray format while the other side of disc is used for recording data in HD-DVD format. Warner Brothers released the first blu-ray/HD-DVD hybrid disc in 2007, however, hybrid discs failed to make any significant impact on the video market as most studios preferred either HD-DVD or blu-ray format. It is less likely that you will find a movie on a hybrid disc.
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