Blu-ray Disc Specs
BD Facts to Know
Now that you know the basic technology behind it all, let us have a look at what the numbers can tell us. The following figures are taken from the specification documents of both technologies. Let's see what they say.
Optics
| Specification | Blu-Ray Disc |
|---|---|
| Laser wavelength | 405nm |
| Numerical aperture (NA) | 0.85 |
| Read power | 0.35mW |
A conventional DVD uses a red laser which has a wavelength of 650 nm while Blu-ray Discs use much shorter wavelengths.
Disc Metrics
| Specification | Blu-Ray Disc |
|---|---|
| Hard coating | Yes |
| Cover Thickness | 0.1 mm |
| Disc Thickness | ~1.1 mm |
| Track pitch | 0,32µm |
| min. pit length | 160.0nm (23.3/46.6GB) 149.0nm (25,0/50.0GB) 138.0nm (27,0/54.0GB) |
The larger the NA the smaller track-pitch and the smaller the pit length the more data can fit on a disc. So it's easy to understand why one disc type can store more than another.
Storage Capacity
The more layers a disc has the more data can fit on it. The thicker the disc (excluding the protective cover) the more layers are possible.
| Specification | Blu-Ray Disc |
|---|---|
| Data transfer rate | 36Mbps (1x) 72Mbps (2x) 54Mbps (video BD-ROM) |
| Video compression | MPEG-2 MPEG-4 AVC VC-1 |
Both next generation disc technologies will support the same video compression technologies including the new MPEG-4 AVC format.
Something Else You Should Know
In addition to Blu-ray Discs, DVDs can also store high-definition content.
HD/DVD-9 is based on a compression method for red-laser discs. This method allows high definition data to be stored on discs that can be read by conventional DVD drives. Solutions are already available which allow storage of 8.4 GB worth of high-definition data on read only double-layer discs. It is hoped that this technology will allow a smoother transition to the new high-definition technology for people who already own DVD drives.
Versatile Multi-layer Disc (VMD) discs are identical in form factor to standard DVDs and also use red-laser technology. However VMD discs have up to 10 times as many layers as a dual layer DVD. With each layer containing up to 5 GB of data, a single MVD disc could have a theoretical capacity of up to 100 GB. MVD discs with capacities of 20 to 30 GB are likely candidates to first hit the market. MVD discs use the EVS HD standard (the only HD standard in China). VMD discs will be much easier to manufacture and VMD drives are standard drives with a modified decoder part.
