HVD: Holographic Versatile Disc

[Couperin]

Has anyone here heard about the new data storage medium that is being researched? Apparently it'll be able to store up to 3.9 terrabytes of data, which is insane.

Anyway, I checked out this article on Wikipedia to see how it worked...

http://en.wikipedia.org/wiki/Holographic_Discs

...and I don't quite get it.

Here's what I can gather... there are two layers on the HVD, one which is read by red laser light and contains 'servo' data, and above this is a layer with normal data on it, read by a green-blue light. The red light passes through the normal data layer, so there's no interference or other weirdness.

But what I don't get it... how does simply storing servo data on a separate layer manage to free up 3.9 TERRABYTES of data? The green-blue light has a longer wavelength than the blue laser light used to read Blu-ray discs, and they can't store anything near the amount as HVDs will.

So what's going on? And what *exactly* is servo data?

 

[Mech_Engineer]

Your answer lies in the very first paragraph of the Wiki article:

It employs a technique known as collinear holography, whereby two lasers, one red and one blue-green, are collimated in a single beam. The blue-green laser reads data encoded as laser interference fringes from a holographic layer near the top of the disc while the red laser is used as the reference beam and to read servo information from a regular CD-style aluminium layer near the bottom. Servo information is used to monitor the position of the read head over the disc, similar to the head, track, and sector information on a conventional hard disk drive. On a CD or DVD this servo information is interspersed amongst the data.

It would seem to me that the advantage of having the servo information on a different layer is it doesn't take up space on the data layer, making it possible to store more "real" data on a layer.

 

[ravenprp]

Yes, I have heard about the Holographic Versatile Disc (HVD) and its potential for storing large amounts of data. It is definitely an exciting development in the field of data storage.

From what I understand, the HVD works by using holographic technology to store data in three dimensions, rather than the traditional two-dimensional storage used in CDs and DVDs. This allows for a much higher storage capacity.

As for the servo data, it is essentially information that helps the laser locate and read the data on the disc. By separating it onto a separate layer, it allows for more space to be used for storing actual data. This, along with the use of a longer wavelength for reading the data, is what allows for the significantly higher storage capacity.

I'm not an expert on the technical details, but I believe the use of holographic technology and the separation of servo data are the key factors in the increased storage capacity of HVDs. It will be interesting to see how this technology develops and how it will impact data storage in the future.