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HEXUS.lifestyle: But in just raw data storage, Blu-ray is going to be better as it holds more data.
Jim Armour: Looking at the numbers on a bit of paper, you’d think so, but what you need to do is look at the Blu-ray discs and players first, before you make a decision. Let’s go back to the disc construction for a second. HD DVD uses a sandwich method which helps to combat disc warping. Blu-ray doesn’t. It uses a single plastic substrate layer, then adds on the recording material and then top it all off with a very hard Zircon layer. This means that when the disc expands to get hot, it will warp downwards as that Zircon layer isn’t going to budge.
HEXUS.lifestyle: But that’s a uniform direction of warping? Surely as long as you’re ready for it, it won’t make any difference?
Jim Armour: You’d think so, wouldn’t you? But now we have to go back to the lens. Blu-ray uses a 0.85 Numerical Aperture and, with their recording layer just 0.1mm below the disc surface, they’ve got to get the lens very close to the disc surface to be able to focus it tightly enough to give them a 25GB storage capacity. So now you’ve got a Blu-ray lens sitting somewhere between 0.1 and 0.3 millimetres from a disc coated with a substance almost as tough as diamond which, when it warps, can only warp downwards, towards the lens. Guess what happens when you run Zircon over glass at 2000rpm? Sure, your data will be safe but you’re going to need a new Blu-ray lens.
HEXUS.lifestyle: So the Blu-ray system has a built in flaw that could mean you get through Blu-ray players quicker than you do discs?
Jim Armour: It would appear so, yes. The other thing to remember is that Blu-ray discs are very expensive to produce when compared to HD DVD discs, mostly because of the construction methods needed to place the recording layer at the optimum distance from the lens so they can get 25GB of storage space. HD DVD takes a more sensible and robust route, chosen from a combination of factors – disc warping, disc durability, focal point of the laser etc. Plus, the use of better Codecs mean that HD DVD doesn’t even need as much storage space as Blu-ray to achieve the same high-quality video. The lower disc production costs reflect this, too.