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Comment by NKCSS | Hacker News Reader

You are forgetting that the speed at which optical drives can be written is bound by the rotation speed. If you have a single laser of this type and mount it in a traditional drive as we know, it would take over a year to write a single disk :) Still lots to do :)

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Really? Assuming that the rotation speed is the same for a normal disk and this denser format, wouldn't said laser be moving over 250,000 times as much data in the same time period?

At 1X speed, a DVD's data rate is about 11Mbit/s - so at 250,000 times the density, isn't it safe to assume a theoretical data rate of 2.75Tbit/s? Of course, pushing that much data at that rate is another problem...

If my assumptions are incorrect, please let me know - I'm just trying to understand.

52x speed has been the limit for a long time because the outside edge of the CD gets to speeds where it could damage itself. I guess it would need a cushion, like a nearly applied (car/bike) disc brake.

Okay - but I'm not talking about changing the rotational speed.

You're forgetting the square-cube law. Or rather, in this case the linear-square law. Think of each bit as a square, with side length 1/n. Oversimplifying, but the basic principle is there.

The total amount of data the laser goes over in a second is proportional to n - because it's related to how long the laser takes to get from one edge of the square the the other edge. But the total amount of information stored goes up as n^2 - it's related to the area of the square.

Or: to put it another way, the number of tracks also goes up when data density increases.

(This also happens with hard drives over time. Recent hard drives take a lot longer to read or write the entire drive than older ones. See http://tylermuth.wordpress.com/2011/11/02/a-little-hard-driv... for example.)

is anyone else really bothered that the article says CD but it's actually about DVD?

That seems overly nitpicky. It's about a new technique for beam lithography and achieving a smaller feature size than previously possible.

The "1000 TB" is just PopSci extrapolation at this point. If it does happen, it'll be neither a CD nor DVD.

It's actually about optical discs. But "CD" is the vernacular for optical discs. Kind of like "hard drive." Modern laptops don't have hard drives--they have solid-state drives, but people still refer to their storage as a "hard drive."

Hmmm. Maybe you could use a prism/mirror array (like in digital projectors) to use a single laser to write in multiple places at once? (Or rather, in sequence but moving faster than the disc rotates?)

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