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Confused about DVD and how it works?
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Joined: Jan 21, 2005
Posts: 7015
Location: Central Illinois, USA
PostPosted: Sat Mar 04, 2006 11:37 am
Post subject: Confused about DVD and how it works?

This is a pretty good article to clear up any confusion (perhaps..lol) you may have about DVD, Single or Dual Layer DVD and how optical drives work. Wink

ABCs of DVD Drive Abbreviations

by J. Kohrs

The number of different formats available in DVD drives can be confusing to anyone in the market for one. The list is much longer, but to address a few of the common formats, we have DVD-ROM, DVD-R, DVD-RW, DVD+R, DVD+RW, DVD-RAM ,DVD+R DL and DVD±RW. Wow! This list of common formats is long enough, no wonder it’s confusing!

What's with all the Formats?!

The reason for various recordable DVD formats is that no one group owns the technology and different groups have chosen to support one technology over another. There is no industrial standard for manufacturers to reference, so for the time being consumers will have a few choices.

The first thing to address is DVD itself, which stands for Digital Versatile Disc. Some may argue that the V stands for Video, but with the capability to store video, audio, and data files, Versatile is definitely the keyword.

Start with the Basics

A DVD-ROM drive is the only one we will address that does not record. ROM stands for Read Only Memory, and refers to the typical drive that can merely read DVDs, as well as CDs (all DVD drives can read CDs). The Lite-On LTD-163-DO-R has attributes representative of your typical DVD-ROM drive, and features a maximum DVD read speed of 16x and a maximum CD read speed of 48x.

Before getting into the different recordable formats, let’s address the basics of what the R and RW stand for, regardless of whether there is a + or – in the middle. R stands for Recordable, which indicates that the disk may be recorded to only once. RW stands for ReWritable, which indicates that the disc may be recorded to more than once, and are generally rated for 1000 rewrites under good conditions.

The DVD-R/-RW format was developed by Pioneer, and was the first format compatible with stand alone DVD players. The group that promotes the technology calls itself the DVD Forum, which is “an international association of hardware manufacturers, software firms, content providers, and other users� with notable members such as Hitachi, Samsung, and Toshiba. The DVD-R/-RW format is based on CD-RW technology and uses a similar approach to burning discs.

The DVD+R/+RW format is a newer format, also based on CD-RW technology, and compatible with a large percentage of stand alone DVD players. The +R/+RW technology is not supported by the DVD Forum, and its main backing comes from a group called the DVD+RW Alliance. The Alliance “is a voluntary group of industry-leading personal computing manufacturers, optical storage and electronics manufacturers� with members such as Dell, Hewlett Packard, Sony, and Phillips Electronics.

The DVD-RAM format is based on PD-RW (Phase-Differential) drives, and actually uses a cartridge to hold the media (just like its PD-RW predecessor). Some DVD-RAM cartridges are double sided, making them ideal for companies to use as system backup, hence DVD-RAM is usually found only in commercial applications, and most end-users won’t ever need to use or see this type of drive. The DVD-RAM standard is also supported by the DVD Forum just like the DVD-R/RW format. However, because of its use of a cartridge (limiting it’s compatibility), and the scarcity and price of the media used, DVD-RAM is a distant third when compared to the DVD+R/+RW and DVD-R/–RW technology.

The +R/+RW and –R/-RW formats are similar, and the main difference DVD+R technology has is the ability to record to multiple layers (with its new DVD+R DL format), where DVD-R can only record to one layer (not all +R drives are capable of dual layer burning, but no -R drives are). The Plextor PX-504U is an example of an external DVD+R/+RW drive capable of recording single layer discs in the +R/+RW format, but also able to read discs recorded by a DVD-R drive.

What is DVD±RW?

DVD±RW is not actually a separate format, but the designation given to drives capable of both –R/–RW and +R/+RW operation. This type of drive is typically called a “Dual Drive� (not to be confused with a “Double Layer� drive) since it can write to both the +R/+RW and –R/–RW formats. The Samsung TS-H552 is a DVD±RW drive capable of reading and writing every format discussed so far, and then some. It takes advantage of DVD+R DL (Double Layer) technology available with the +R format, allowing the appropriate media to store virtually double the 4.37 GB capacity of a typical single layer disc.

The other main thing to consider with DVD burners is selecting the correct media. Media for DVD-R, DVD-RW, DVD+R and DVD+RW media may all look the same, but they are slightly different in order to match the specific recording formats. The price of media for either format is generally the same, with RW media costing a good deal more than R media of either format. Double Layer media is even more expensive, and is the only way for an owner of DVD+R DL drive to take advantage of the tremendous capacity increase. As the amount of Double Layer drives increase in the market, the price of the DVD+R DL media is expected to fall with increased production of the media. DVD Burners (as these drive are often referred to) can be picky about the media supported, so be sure to choose your media wisely.

DVD in a Nutshell

DVD-ROM : Reads DVD discs
DVD+R : Writes to DVD+R media (will also typically write to CD-R and CD-RW media)
DVD+RW : Writes to DVD+RW media (will also typically write to DVD+R, CD-R and CD-RW media)
DVD+R DL : Writes to DVD+R DL (Double Layer) media (will also typically write to DVD+R, DVD+RW, CD-R and CD-RW media; many Double Layer drives are ALSO dual drives – that is, able to write to BOTH +R/RW and –R/RW media)
DVD-RAM : Writes to DVD-RAM cartridges (not in wide use on consumer market – mainly a business format; can also read PD-RW discs. Will not usually be able to write to any other format including CD-R or CD-RW)
DVD-R : Writes to DVD-R media (will also typically write to CD-R and CD-RW media)
DVD-RW : Writes to DVD-RW media (will also typically write to DVD-R, CD-R and CD-RW media)
DVD±RW : Writes to DVD-RW and DVD+RW media (will also typically write to DVD-R, DVD+R, CD-R and CD-RW media; typically called “Dual Drives� since it can burn to two different DVD formats)

Final Words

This article took a look at the more common formats of DVD drives in order to shed some light on all the choices available. The differences between them all may be subtle, but the compatibility issues can be quite frustrating. The simple answer to anyone considering a drive is to forget about + and – by themselves, and shoot for universal compatibility with a good DVD±RW with DVD+R DL support.

J. Kohrs second update article...

Double layer DVD writers and the blank discs for them were just hitting the market then so he didn’t have much to say about the latest and largest-capacity optical disc system. Since then, DL drives and media have popped up all over at decent prices so it’s time to dig a little deeper.

That last sentence is a bit of a pun on the whole double layer thing because it works by burying your data a little deeper into the disc. We’ll discuss why double layer is so exciting, and when you can economize by using the less expensive single layer discs.

1. Refresh on How DVDs Store Data

Most explanations of how optical discs work start with an allusion to LP records with a track that spirals across the face of the disk and a pickup the follows the track to extract the data stored there. Unfortunately, the flat disc and the spiral are about the only things in common.

Optical discs like CD-ROM and DVDs are made up of a clear plastic disc with a layer of very thin metal buried just under the surface of the plastic. The track is actually molded into the plastic, a thin metal layer is laid over the plastic, and the whole thing is sealed up with a clear lacquer finish.

2. Not Grooves: A Trail of Bumps

LP records are easy to visualize because they use a V-shaped groove that forms the track. The sharp point of the pickup fits down in the groove and the groove wall pushes the pickup to keep it tracking the spiral. Optical discs are completely different, with a laser light focused into the spiral track of bumps. An optical sensor picks up the reflections of the bumps and electronic tracking circuits command tiny motors to move the pickup to keep it aligned with the track.

Notice I said track and not tracks? There is a single track that starts at the inside near the center hole and spirals out, just the opposite of the LP record. It’s not concentric tracks like a hard drive or floppy disk. The disk could be any size up to the maximum of 120 millimeters, about 5 inches. There are smaller optical discs available, all the way down to business card-sized with only a few dozen Megabytes of storage.

Speaking of tracks and dimensions, they pack almost 8 miles of data in that single track. The double layer DVD disc has about 15 miles of storage track. That means the track has to be wound pretty tight with a pitch of only 0.74 micrometers (millionths of a meter) between them. That takes some pretty precise tracking!

3. Ones and Zeros Become Lands and Bumps

Along the track, there are flat reflective areas called lands. This is really just the non-bumped part of the disc surface. Then, there are the non-reflective bumps. A flat reflective area represents a binary 1, while a non-reflective bump is a binary 0. The DVD drive shines a laser at the surface of the DVD and can detect the reflective areas and the bumps by the amount of laser light they reflect. The optical pickup converts the reflections into 1’s and 0’s to extract digital data from the disc.

This describes how commercially-pressed audio CDs, CD-ROMs and DVD movies work. They are read-only devices with the simplest construction and are the easiest to explain. A recordable disc, however, also needs to allow the drive to write data onto the disc.

In order for a recordable DVD-R or DVD+R disc to work, there must be a way for a laser to create a non-reflective area on the disc. These discs have an extra layer that is a dye that can be changed by shining a strong laser beam on it. On a blank recordable disc, the entire surface of the disc is reflective. The laser can shine through the dye and reflect off the metal layer. When the drive writes data to the disc, the laser heats up the dye layer and changes its transparency, which is the equivalent of a non-reflective bump.

4. The Trick of Double layer

Now we know how a single layer DVD works, both the prerecorded type and the ones you can burn at home. Just how the heck do they put two layers of data on one side of the disc? It would be real easy to say magic at this point, but the real explanation is pretty simple.

Think about how when you walk up to a window with a screen and look out that you see the scene outside and don’t even see the screen. It’s close to your face so it’s out of focus and you don’t even notice it is there. If you back up a little and force your eyes to focus on the screen, it pops right out and you can see it and the scene outside is all a blur.

Double layer DVDs pull a similar trick. There is only one reflective layer, but there are two layers of dye where the actual data is stored. The lens in the pickup focuses the beam on the top layer to read the first bunch of data, and then the lens focuses the beam on the bottom layer and sees right through the top layer. Because the top layer is out of focus, the data stored there just disappears and the bottom layer is read instead.

All that build up and detailed explanation to find out it’s a simple trick of optics that even your own eyeballs can do!

5. So What’s the Benefit?
When recordable DVD media first hit the market, it hadn’t grown up yet and capacity wasn’t too much bigger than CD-R. As DVD-R and DVD+R came of age, the capacity of a single-sided disc settled on 4.7 Gigabytes. That was enough room for a two-hour medium resolution compressed movie. It’s also a handy size for normal backups of your hard drive or all the digital photos from your vacation even if you shot them all in high quality mode.

But, what if you want to record a truly high definition movie? It won’t fit in 4.7 Gigabytes. Even a medium definition movie won’t fit if it extends past two hours. How many movies come with a separate disc for the extra features? It’s a pain to have to get out of the easy chair to change discs. The double layer DVD solves this by having 8.5 Gigabytes of storage without having to flip the disc.

6. What Do I Need?

Naturally, older DVD drives don’t have the mechanism to switch focus between the two levels of a double layer disc. The pickup has to be physically moved to change the focus point from top to bottom, so you need a drive with this built in. The LG 16x Double Layer DVD±RW/DVD-RAM IDE Drive is typical and attractively priced. Computer drives that can read double layer usually also write double layer and that’s the case here. Be aware that double layer DVDs have to be written at the 4X speed as opposed to the 16X for single layer discs.

7. Blank DVDs Are a Bargain

CD-R media are really inexpensive these days, with recordable DVDs being a little more expensive. But, are they? A single layer DVD-R or DVD+R can hold as much as seven CD-Rs. That means that if a DVD is less than seven times more expensive, it is actually cheaper than a CD-R for those large data storage tasks. They are also a lot more convenient than shuffling a stack of CD-Rs in and out of your drive.

If you just want to test the waters without springing for a tall spindle of blank double layer DVDs, try the Verbatim Double Layer Solution Kit (DVD+R, DVD+R DL, DVD+RW) , which gives you a sampling of three different blank optical disc types. If your storage needs are less than about 4 Gigabytes, then stick with the single layer discs.

8. HD DVD versus Blu-Ray

While double layer DVD seems like a huge amount of storage, the requirements of super high definition video and huge hard drive backup push the optical drive manufacturers to even larger capacity discs. HD DVD is a refined version of the DVD we use now. It uses the same trick of double layers to almost double the capacity up to 30 Gigabytes per side; backing up a full image of a 160 Gigabyte hard drive takes a half dozen discs.

Blu-Ray answers this with the promise of up to 200 Gigabyte discs eventually becoming available. They pack the data in even tighter than HD DVD and can stack up several layers to increase storage.

Unfortunately, HD DVD and Blu-Ray will probably be only available as commercially produced DVDs for viewing movies for the near-term. Somewhere down the road, we’ll start seeing recordable versions to mount in our computer’s drive bays.

Final Words

While recording movies on single layer DVDs might be fine with the old standard TV, now that you have a widescreen flat panel television that is capable of HDTV, why suffer degradation of image quality by over-compressing the video? Get a double layer DVD drive for your computer and stock up on double layer DVD blank discs to capture all the detail.

The same goes for your computer backups. Put your whole photo collection on one 8.5 Gigabyte double layer disc. Don’t worry about running out of space on a single disc. Though the double layer discs may be more expensive, they hold twice as much and take up less storage space than a pair of single layer discs or a dozen or more CD-Rs.

The Blu-Ray is getting quite a bit of contorversy and since Sony is involved, most think they're up to something...(remember the root kit thing?) Still, if it hits the masses, and it will sooner or later, storage such as CDR's will soon fall into the "A" drive pit... Wink
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Joined: Mar 07, 2005
Posts: 6475
Location: 3rd Branch up, 'Ye Olde Oak', Green Wood.
PostPosted: Mon Mar 13, 2006 6:47 pm
Post subject: Re: Confused about DVD and how it works?

It's not only Sony involved in Blue-Ray but they have taken a massive lead in the tech race which is why they're getting all the publicity.
They've managed to record 2Gb of information onto a piece of tissue paper.
Now, a tissue paper is not the best medium to deal with the sort of data we deal in but, if they can do that with tissue paper, you can imagine the possibilities of doing the same with the blue ray equivalent of a cd style data carrier.
It's already out-performing the write speeds of current equipment.
The most likely covert / sinister activity I reckon is going on is that the sob's have all this technology ready to go right now and are holding off so they can shift their old cd/dvd hardware stock out to us poor sob's, who then have to buy Blue-Ray replacements.

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PostPosted: Mon Mar 13, 2006 10:55 pm
Post subject: Re: Confused about DVD and how it works?

Yall might be interested in this too.
WITH ALL THE FUSS going on between the Blu-ray and HD-DVD camps, here in Hangover, news of the third way, EVD, is starting to emerge.
London-based firm, New Medium Enterprises, got together with Beijing-based E-World Technology, to define a standard which now has a support from around 10 other companies, mostly located in mainland China.

The Enhanced Versatile Disc is a new High Density standard with a far more reasonable price expectation for both media and players. EVD media has less capacity than either Blu-ray or HD DVD - but it's cheaper and has already become the optical disc standard in China. It is expected to become a major player across developing markets.

Although the standard is currently read-only, E-World expects to release a recordable version by CeBIT 2007.

The makers said they were looking to switching the red laser for a blue one, once the blue-laser technology matures and comes down in price.

Anyone recall the outcome of the JVC / Betamax saga? lolol

Skwerl's place.

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AUDIO > Creative X-Fi Xtreme Music (plus - Universal Audio UAD2 Quad Custom accelerator);
HDD > 3x1TB+ M.2. SSDs; LCD > DELL - S2419HGF (1920x1080);
PSU > 650W be quiet Straight Power 11 - 80+ Gold;
CASE > BeQuiet! SILENT BASE 601; OS > Windows 11 Home Advanced (64-bit).
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PostPosted: Thu Nov 24, 2011 6:35 pm
Post subject: Re: Confused about DVD and how it works?

With all of that taken into account I think I will scrub the idea of making a DVD double sided disk to hold the download UP 3.0RC4 and the Mega download for my squad members. First I don't have a DVD drive to support a 2 sided format and who knows what each squad member has in his or her's computer.

A midair collision can ruin your whole day
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