| ||The Blank Truth|
This week's tech tip examines blank CDs and DVDs, giving you a layer-by-layer introduction into how the technology works, and how to make it work for you.
How Optical Media Works
"Optical" media uses light to save and read information. When someone mentions "optical" media, they usually mean either a CD or a DVD.
Regular CDs (and DVDs), are made of several layers. On the top and bottom are pieces of plastic. Sandwiched between the plastic layers is a layer of aluminum or some other reflective metal.
Information is stored as tiny bumps punched onto the top layer of the CD. The bumps are lined up in an amazingly tight spiral all around the CD, kind of like the grooves on an old-style vinyl record. But unlike a vinyl record, variations on the surface of a CD represent 1's and 0's.
The layer of aluminum (or some other reflective metal) is then pressed against the plastic, so thinly that the bumps are still "visible" to the laser beam in your CD through the aluminum layer. The CD player shines its laser on the CD as it spins, "reading" the reflections off the bumps and translating them into information.
|How a CD-R Works |
A CD-R/DVD-R looks like a regular CD, but it's made of different stuff. Between the plastic layers of a CD-R is a thin layer of a special dye that reacts to the laser in your CD burner. When the laser shines on this dye, it changes, chemically. The laser "burns" a tiny spot in the dye. When your CD player reads the CD-R, it thinks the tiny spot is a bump on a regular CD and interprets the bump as a 1 or 0.
+ vs. -
Some blank CDs are CD-R, some are CD+R. DVDs come in DVD-R and DVD+R too. The + and - are different ways of doing the same thing. In the early days of CD-R technology, there was a lot of competition between the formats. There was never a truly clear winner, so most manufacturers just started making sure their equipment supported both.
They sound the same, they store the same amount of information, and the vast majority of players support both + and - discs. Check your player's manual to be sure, but when shopping for blanks, the biggest hassle you're likely to encounter is accidentally getting CD-RW instead of CD-R.
R vs. RW
A regular, old CD-R or DVD-R can have information written to it only once. CD-RW (and DVD-RW), on the other hand, can be written and rewritten many times. However, if you need your information to stay written, CD-RW isn't the best way to go. Although CD-RW is a very stable, reliable technology, the information on a CD-RW disc probably won't last as long as a regular CD-R.
Also, if you're buying discs to make audio CDs, make sure the CD player you want to listen on is compatible with CD-RW—many aren't.
CD vs. DVD
The CD came, and there was much rejoicing among consumers. Then a few years later the DVD arrived. It's no coincidence—DVD technology builds on CD technology.
A CD holds up to 700MB of data. A DVD can hold much more—anywhere from 4GB to almost 16GB! That's the most obvious difference. There are also more flavors of DVD-R than CD-R. More about that later.
DVD - The Next Level of Storage
They're about the same size, they look awful similar, and yet a DVD can hold so much more than a CD (800MB vs. 4.4GB for a regular DVD). How does it do that?
A DVD is similar to a CD in how the information is stored, but it's like the difference between a Model-T and a '65 Mustang. Remember that information on a CD is stored as "bumps" on the surface of the CD? Well, on a DVD the bumps can be much smaller. And the spiral of bumps that winds its way around the disc is much tighter on a DVD, with much smaller space between rings. It's a spiral a quarterback would kill for!
Even More Storage: Dual-layer DVD
And there's another advancement that takes DVDs to yet another level of storage. The "dual-layer" (sometimes called "double-layer") DVD sandwiches two layers of information on the same disc, to hold almost 8GB of data! This compares with 4.4GB for a single-layer DVD. To get even more space, you can buy double-sided dual-layer DVDs!
But before you swear to buy nothing but dual-layer DVDs, make sure your DVD burner is compatible. Dual-layer DVD-R is the cutting edge right now, so you'll pay a premium for both the blank discs and a compatible DVD burner.
Finding the Best Blanks
As we mentioned in the introduction, there are lots and lots of different brands of blank discs. How do you know which to buy? Well, it depends on your needs.
You Get What You Pay For
If you use CDs for temporary storage, not intending them to last, you can probably get away with buying the cheapest pack at the store. Cheap CDs and DVDs aren't manufactured as well, tend to fail when you're trying to burn them, and they're not as durable.
So don't use a cheapo for anything you care about, or if you expect the burned CD to take a beating. Cheap CDs can last a good while, if you're lucky. Most estimates are 5 to 10 years for even the best standard blank. The cheap kind may fail long before that—and of course, when it's most inconvenient.
The High Road
Move up a notch in price, and your burned CD can take more abuse, and it'll last much longer. Most experts recognize Taiyo Yuden as the best brand when it comes to blanks for everyday use (see the next section for the best brand for extraordinary use.) Taiyo Yuden manufactures blanks for other companies as well as selling their own brand. Look for Fujifilm or Maxell; if the pack is marked "Made in Japan," it was almost definitely manufactured by Taiyo Yuden.
The Mount Everest of Blank CDs
Mitsui Advanced Media America ("MAM-A") makes archival blank CD-R media that is designed to last over 100 years! They use real gold for their reflective metal layer (gold doesn't corrode), and a special patented dye for burning. And they're made in America. Colorado Springs, to be exact.
How to Store a CD Forever
So you've got wedding photos, and you've scanned your grandmother's old photo albums, intending to create a digital archive of your family. What's the best way to help ensure those precious memories are never lost?
There's Always Analog
- Make more than one copy. Keep them in different places, in case of fire, flood, earthquake, locusts, etc.
- Use a Mitsui Gold blank CD-R (Maxell has a similar product).
- Burn the CD at the slowest speed your burner will allow. 4x or 8x is good. This helps reduce any tiny errors that may creep onto the CD at higher speeds.
- Store the finished CD in a cool, dry place. Some banks store their vital backup CDs in safety deposit boxes. That's the ultimate in climate-controlled storage—cool, dark, and with very low humidity.
Keep in mind that CDs themselves have only been around for a little over 20 years. No one really knows how long a CD-R might last, no matter how many scientific tests are run.
So if you're storing photographs or really important documents (like a will), why not print them out and store the prints somewhere safe? It's possible (some would say likely) that in 100 years CD players will be obsolete and your carefully preserved CD-R won't be readable. But a printed picture will be useful and beautiful as long as people have eyes to see it.
Learn More About CD and DVD Technology