MaximumPC 2006 04

T

he consumer electronics market hasn’t

seen a fi ght like this since the legend-

ary Betamax vs. VHS wars of the 1970s. In

one corner, we have HD-DVD, developed

by Toshiba and NEC and supported by a

coalition of heavyweights including Universal

Studios, Intel, and Microsoft. And in the

other, we have Blu-ray: a Sony invention

endorsed by an equally impressive roster

including Disney, Fox, Apple, and Dell.

The prime impetus for both technolo-

gies is storage capacity: Current-generation

DVDs are inadequate for high-defi nition

video. The two technologies share a number

of characteristics, too: Both use media that,

from all outward appearances, looks identi-

cal to today’s CDs and DVDs. Both replace

the red laser used in CD and DVD drives

with a blue-violet laser. And both promise

massively increased storage capacity.

But that’s where the similarities end: The

two technologies are fundamentally differ-

ent and—more importantly—fundamentally

incompatible. And once consumers voice

their preference (a decision that will undoubt-

edly be shaped by the actions of movie stu-

dios and hardware manufacturers), it’s quite

probably game-over for the other contender.

THE LOWDOWN ON HD-DVD

HD-DVD is a far more evolutionary technol-

ogy than Blu-ray. An HD-DVD is 12cm in

diameter, just like a DVD, with a 1.2mm-thick

substrate sandwiched between two 0.6mm-

thick layers of transparent polycarbonate. A

single-sided disc features a refl ective data

layer on one side of the substrate, with a

shallow spiral groove extending from the

hub to the outside edge of the disc.

If you were to examine this groove under

a microscope, you’d see that it consists of a

sequence of microscopic “pits” and “lands,”

just like any other optical disc. Your disc

drive spins the disc while projecting a fi nely

tuned laser through the polycarbonate and

onto the substrate. The pits absorb light

and the lands refl ect it; an optical pickup

monitors the transitions between the two.

HD-DVDs are capable of storing three times

more data than DVDs thanks to the width of

their grooves (commonly referred to as track

pitch) and the size of their pits and lands.

With a track pitch of just 0.40 microns,

an HD-DVD’s grooves can be packed much

more tightly together than those of a DVD,

which has a track pitch of 0.74 microns. But

the track pitch isn’t all that’s been shrunk;

the pits on an HD-DVD disc are nearly half

the size of a DVD: 204 nanometers each,

compared to 400 nanometers on a tradi-

tional DVD. These factors contribute to an

HD-DVD’s ability to store 15GB of data in a

single layer, compared to a DVD’s 4.7GB-

per-layer capacity. Add another layer to the

same substrate and you double HD-DVD’s

capacity to 30GB; place a two-layered sub-

strate on the other side of the disc and you

get 60GB of capacity.

Smaller grooves and pits and lands

require a higher-precision laser, and that’s

the second half of the equation for both

HD-DVD and Blu-ray technology. While CD

drives are equipped with a 780-nanometer

wavelength red laser, and DVD drives uti-

lize a 650-nanometer wavelength red laser,

both of the next-gen optical formats use a

405-nanometer blue-violet laser for an even

tighter focus. The numerical aperture of

the optical lens through which the laser is

directed is almost as critical as the laser’s

wavelength. As with microscopes, tele-

scopes, and cameras, the larger the optical

drive’s lens aperture, the more light it will be

capable of gathering and the more it will be

r & d BREAKING DOWN TECH —PRESENT AND FUTURE

60 MA XIMUMPC APRIL 2006

White Paper: Blu-ray and HD-DVD

The battle for supremacy of the

next generation of optical-disc

technology is about to begin.

Here’s our pre-fi ght analysis

of the competing standards

BY GORD GOBLE

HOW IT WORKS Next-generation optical disc formats

ÑHow do you fi t more data in the same space? Pack it tighter and use more precise tools to read it. HD-DVD and Blu-ray drives

replace the red laser used in CD and DVD drives with a blue-violet type with a shorter wavelength. This enables disc

manufacturers to shrink the size of the pits used to represent data.

Blu-ray goes one step further: It places the data surface closer to the laser, so the disc pits can be even smaller. A Blu-ray

disc can store 25GB of data in the same space that HD-DVD uses to store 15GB.

LASER SPOTS TO SCALE

DATA SURFACES TO SCALE

DISC CROSS SECTIONS VERTICALLY TO SCALE

1.6 micrometers 1.1 micrometers

0.62 micrometer 0.48 micrometer

Data surface Data surface

Label Label

CD DVD HD-DVD BLU-RAY