One of the most widely used and popular pieces of technology on the planet, DVDs have changed the way we watch movies at home, the way we store data and the way we play music.
What’s in a Name?
There is some debate about what the term “DVD” actually stands for. The generally accepted definition is “digital versatile disc” (as the discs can be used to store information other than video). “Digital video disc” is another popular interpretation. There are others though who claim that “DVD” is a term in itself and doesn’t stand for anything.
Regardless of it’s name, the product itself was an exponential leap in terms of data storage from its cousin, the Compact Disc. Whereas a CD can hold 650MB of data, the standard DVD has a capacity of 4.7 GB.
DVDs – A History Lesson
Old enough to remember the Betamax-VHS war in the 1980s? Well, it almost happened again with DVDs. In 1993, two high-definition optical storage formats were under development:
The MultiMedia Compact Disc (MMCD), backed by Sony and Phillips.
The Super Density Disc (SD), backed by Toshiba, Time Warner, Matsushita, Hitachi, Mitsubishi, JVC, Pioneer and Thompson.
Fortunately, the computer industry got wind of the approaching format war and threatened to boycott both formats, demanding a single, combined format instead. The two development groups bowed to pressure, amalgamated features of both discs, and, in 1996, introduced the DVD format we know today.
Consumers were saved from having to choose between an SD or an MMCD player, and computer manufacturers avoided having to accommodate both formats into their machines. Whew!
In the realm of recordable DVDs, though, things aren’t quite as homogenous. There are two sub-formats available today: DVD-R and DVD+R. You’ve stood in Dick Smith’s wondering what the difference is, right? Suffice to say it’s rather technical and has to do with differences in things such as tracking, speed control and error management.
Until 2003, when multi-format DVD burners began to be introduced, it was necessary to choose a blank DVD that matched your burner. Now, as almost all machines are capable of burning both formats, and the general user won’t discern any difference in performance anyway, it doesn’t matter whether you choose + or -.
Further DVD Variations
Beyond the + and – differentiation, there are a couple of other DVD variants. While DVD-R and DVD+R are single-use discs, DVD-RW and DVD+RW are rewritable, meaning you can record over what you’ve already recorded as many times as you like.
Dual layer discs (DVD-R DL and DVD+R DL) have a double layer of recordable material and can hold almost twice the amount of information as a standard DVD.
Double-sided discs have recordable material on both sides of the disc.
But How Do They Work?
A DVD disc has a base layer of polycarbonate that carries a spiral track of microscopic pits and “lands” (flat parts of the disc between the pits). This track runs outwards from the centre, to the edge of the disc. The polycarbonate base is covered with a layer of reflective material, which is itself covered with a clear protective layer.
When the disc is inserted into a DVD player it is spun at a precise speed and a laser tracks across it, following the spiral track and reading those pits and lands. The laser beam bounces off the reflective material into an opto-electronic receptor which detects minute changes in light.
Computer technology within the player then decodes these changes into video and audio signals.
The reason a DVD can hold so much more information than a CD is that on a DVD the pits are half the size, and the tracks are twice as close together.
How Long is My Data Safe?
Manufacturers claim a 100 year life-span for single use recordable DVDs and 30 years for rewritable discs.
What Does the Future Hold?
In a nutshell, increased storage capacity.
In 2006 Blu-ray was introduced, the victor in a next-generation format war with its opponent HD DVD. Dual-layer Blu-ray discs offer a storage capacity of 50 GB.
Further down the track, even greater storage will be possible. Technologies under development include the Holographic Versatile Disc which may one day hold as much as 3.9 terabytes of information, and 5D DVD, a multi-layer, multiple laser system that boasts the possibility of 10 terabytes of storage.
So, next time you pop in a disc and settle down to a movie, spare a thought for the technology at your fingertips. We watch movies now with greater clarity and definition than any previous generation. We store data in amounts unimaginable a decade ago. The machines that make this happen, though we often take them for granted, are marvels of ingenuity and engineering.
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Tags: computer industry, computer manufacturers, data storage, density disc, digital versatile disc, digital video disc, DVD-R, DVD+R, format war, multimedia compact disc, optical storage, storage formats, video digital