How dense is information stored by lasers compared to magnetic technology?

[MadRat]

I'd think that laser technology would have started outstripping magnetic storage technology by now. So far it looks like they are sticking far more information on magnetic storage platters of comparable size.

Does anybody have any direct comparison information?

 

[Mookow]

no direct comparision info, but assuming both DVD's and HD platters are 3.5 inches wide, magnetic is far ahead of laser, as a DVD hold 6.4Gig's (or something like that), while recent IDE drives hold 20 Gigs/platter

 

[grant2]

Why would you think that? Do you actually know the technologies or is it a gut feeling?

 

[purplecow]

"assuming both DVD's and HD platters are 3.5 inches wide, magnetic is far ahead of laser, as a DVD hold 6.4Gig's (or something like that), while recent IDE drives hold 20 Gigs/platter"

 

[spanner]

Um, DVD's can hold upto 15gigs if I remember correctly and they are not double sided like hard drive platters. I think the problem with optical is the speed.

 

[HaVoC]

Double sided, double-layered DVDs hold 18GB but that is still far less than your 20GB/platter HD. The DVD needs 4 surfaces to get 18GB but the HD does it only in 2 which is roughly twice the density.

I'm no storage expert but I feel the advantage to the HD is the enclosed environment allows for very close bit packing which translates into an incredible amount of bits/sq in. Optical drives have to read and write under much more variable circumstances and distance from head to media.

 

[grant2]

Double sided, double-layered DVDs hold 18GB but that is still far less than your 20GB/platter HD. The DVD needs 4 surfaces to get 18GB but the HD does it only in 2 which is roughly twice the density.

I'm no storage expert but I feel the advantage to the HD is the enclosed environment allows for very close bit packing which translates into an incredible amount of bits/sq in. Optical drives have to read and write under much more variable circumstances and distance from head to media.

I still haven't seen any of these mythical double-sided, double-layer DVDs despite the spec being around since 97. The fact is that double-layer is easier said than done, and just like double-sided DVDs was only included in spec to appease a certain faction so they could actually finalize it.

And you're dead on the variability aspect, in a sealed HD case you can push tolerances to the max, but with a disc you have to account for dust, scratches, variations in spin rate, laser alignment, etc. Not to mention that a very large portion of data on DVD and CD are devoted to error correction and framing.

finally, HD mfg'ers can push ahead with new technology as soon as it's perfected, on the other hand optical discs are stuck in standards that appear to change about every 15 years.

 

[Adul]

a lot of current DVD are using double layer. You may notice a skip somewhere in the movie, that is when the transition to the other layer happens. Some movies hide it better then others. Just pay attention.

 

[Sohcan]

<< I still haven't seen any of these mythical double-sided, double-layer DVDs despite the spec being around since 97. The fact is that double-layer is easier said than done, and just like double-sided DVDs was only included in spec to appease a certain faction so they could actually finalize it. >>

Ummm, yeah...most of the new DVD movies that I've bought/rented in the past year have been double-layered. And I did see a double-sided DVD once (I think it was Starship Troopers?)...one side was pan &amp; scan, the other side was widescreen.

 

[NTB]

<< And I did see a double-sided DVD once (I think it was Starship Troopers?)...one side was pan &amp; scan, the other side was widescreen. >>



A River Runs Through It is like that too - double sided; with one side being pan'n'scan and the other being wide-screen. So they are out there.

 

[cvlegion]

I am assuming if they wanted to they could make an optical drive a lot more dense than your magnetic drive. It is simply by making the pits smaller and using a small wavelength laser. They could use a laser that emits ultraviolet light if they needed to. However, what is the point? Store 10 movies on a disk and risk a totally new optical format. When we have DVD writers for the same amount as CD writers then DVD will hold an immense amount of data. Also they keep on researching multi-layer CDs (I mean many layers). That is another way to attain a huge amount of data on a disk. There it is simple diffraction theory (physics).

The thing with magnetic drives. There is a limit that magnetic drive have. They have to stay magnetized and they cannot leak magnetism to other sectors. This means there has to be a certain amount of separate between sectors for how strong the magnetism of the strong are. If you see what I am getting at: Optical drives there technical limit is with the intensity and type of laser they use (cost factor come in to play) but with magnetic drives are are going to be physical restrictions on density.

 

[HaVoC]

yes but you raised an important point which is STANDARDS. Necessarily a standard for removable storage will reduce the innovation and pace of improvements for that technology. HD just need to have a standard interface (IDE, SCSI, etc) which can be totally abstract from the technology actually reading the bits. Hence you can really push the technology generation to generation.

<< I still haven't seen any of these mythical double-sided, double-layer DVDs despite the spec being around since 97. The fact is that double-layer is easier said than done, and just like double-sided DVDs was only included in spec to appease a certain faction so they could actually finalize it. >>

I haven't seen the DS/DL but dual-layer discs are pretty common as many are over the 4GB for a single side, single surface. Maybe the DS/DL are too expensive to manufacture and since movies are 95% of the market for DVD storage, there is not currently a need for larger DVDs. But the 18 giggers could conceivably hold HD DVD movies, I suppose.

Correct me if I am wrong, but in &quot;The Matrix&quot; there is a layer change at the scene where Crypto betrays Neo and Morpheus by dropping the cell phone in the trash can. (somewhere right around that scene)