Optical Media Explained

MASHMALLOW FOOD DEMO

- Call for Help Episode #85 (3 minutes ain't enough)

- Typically, the laser will actually hit the disc from the bottom, as the label side is usually on the top.

- Techically, 0's and 1's are created by the Transitions between puts and lands, but you get the idea.

- A pit reflects light more dimly than a land, and a diode is used to measure the difference in reflectivity.

- Though the shape of the disc is the same, data CS's , Audio CD's, DVD's all have a different sata structure.

- Master "stampers" are made from a glass master with nickel coating, with the pits burned into an emulsion layer.

- Unlike old-school vinyl records, data on CD's and DVD's starts on the inside, and moves outwards.

CD-R = Compact Disc Recordable
- Burnable Media uses a special layer of dye that changes properties when hit by the "write" laser.

CD-RW = Compact Disc Re-Writeable
- about 100 re-writes per disic
- The alloy used for CD-RW is typically comprised of silver, indium, antimony and tellurium, or AglnSbTe.
- The burning process melts the alloy into an amporphous state. Erasing data anneals it back to cyrstalline.

The two most common sizes of CD
- 650 MB (about 74 minutes)
- 700 MB (about 80 minutes)
- CD's use a 780 nanometer wavelengh.
- Beyond 700 MB, media may be unusable on older machines,as the space between data tracks becomes too tight.

Single-Layer DVD = Capacity of 4.7 GB
- more than seven times the size of a CD.
- DVD uses a laser with a 650 nanometer wavelengh.

Dual-Layer DVD = Capacity of X.X GB
- polycarbonate, dye and reflective layers brng the count up to 7 or 8 layers.
- With mulit-layer discs, one of the layers must be semi-transparnet so the laser can re-focus right through it.
- It's like the way a wire screen vanishes when your eyes refocus on an object on the other side of a screen door.

FUN FACT: on a second layer of a dual-layer DVD, the data goes from the outside to the inside, instead.

Next Generation DVD Media:
- HD-DVD is more than three times the size of DVD for a single layer.
- Blu-Ray is more than five times the size.
- HD-DVD is 15 GB per layer, while Blu-Ray discs can cram up to 25 GB per layer.
- A dual-layer Blu-Ray DVD can fit 50 GB of data.
- Triple-layer HD-DVD can handle 45 GB.
- Triple-layer HD-DVD and dual-layer Blu-Ray are still in the development stage.
- So all these numbers could change.

Blu-Ray supporters:
Sony
Apple
Dell
Hitachi
Pioneer
Panasonic
HP
LG
Samsung
Philips
And More!

HD-DVD supporters:
Toshiba
NEC
Microsoft
Intel
Sanyo
Fujitsu
Canon
Imation
And More!

- This minimizes the "stutter" if the DVD player changes layers in the middle of a long motion picture.

- Both HD-DVD and Blu-Ray use a 405 nanometer blue laser to read data from the disc.

- Remember, we are trained professionals. Do not try this at home, unless you're bored.