Chapter One
Optical Storage: It's All in the Pits
In This Chapter
* Defining the disc
* Understanding how stuff is saved on a disc
* Examining the insides of CD and DVD drives
* Understanding the different types of optical media
* Comparing tape, disks, and hard drives with CD and DVD
* Checking your system requirements
* Saving different types of stuff
* Taking care of your discs
When's the last time you really looked at a CD? I mean really stared at it, in rapt fascination? Believe it or not, CDs used to be enthralling!
CDs and DVDs are now both staples of the technical wonderland that you and I live in. Unless you're older and you were around long before 1980 - the days of disco, Charlie's Angels, and Rubik's Cube - you won't remember the lure of the compact disc. In those dark times, before the introduction of CDs, music lived on huge, clunky vinyl albums. Computer software was loaded on floppy disks. Movies? They were kept on videotapes. (Remember those?)
At first, this situation wasn't a bad one - at least until you kept these old-fashioned storage media for a year or two. Suddenly, you would find that those records had picked up scratches and pops. Computer programs were growing so large that they would span five or six floppies. And sooner or later, those floppy disks and movie videotapes could no longer be read reliably; after a mere 100 viewings or so, you would end up buying another VHS copy of Enter the Dragon. (Okay, so I'm a big Bruce Lee fan. Substitute your favorite movie instead.)
Like a circular knight in shining armor, the arrival of the CD heralded the beginning of the digital consumer age. I'm not kidding; I can remember an entire room of technotypes jumping with excitement just to see their first compact disc! (None of us could afford an audio CD player, and computer CD-ROM drives hadn't arrived yet, but it was great just to see a real CD.) In the beginning, audio CDs brought us crystal-clear sound and the convenience of jumping instantly from track to track. Then, computer software suddenly fit on one CD, and the software could always be read reliably. With the advent of DVD, widescreen movies are accompanied by luxuries like alternative soundtracks and interviews with the cast and director. Would you go back to anything less?
In this chapter, I introduce you to the basics of compact disc and DVD storage: You don't have to know all this stuff before you jump into recording your own discs, but if you understand the basics of what's going on, you avoid mistakes. (Always be prepared.) I promise to tell you along the way about what you absolutely need to know. You find out how discs store information, video, and music as well as what's inside your CD or DVD recorder. I cover what types of media you can use and what you can store. Finally, I show you how to properly care for your optical pets. (You may not stare wistfully at CDs like I used to, but you still have to keep them clean.)
Always Begin with a Definition
In this case, let me start by defining the now-familiar term CD-ROM - short for compact disc read-only memory. (I've shortened this to CD throughout this book, which will save about 200 trees by the time I've finished.) This high tech description simply means that a CD stores information of some sort that your computer or audio CD player can read but can't write to (which makes the CD-ROM drive different from a hard drive, for example, which you can both read from and write to). In general, I use the word disc to describe both CD-ROMs and DVD-ROMs; they're both similar, read-only, and look very much alike.
Keep this in mind: Whenever folks refer to just a CD-ROM or DVD-ROM drive (without using the word recordable), they're talking about the drives that just read discs and can't record them.
The basic specifications of both audio CDs and data CDs (those discs you use in your computer) are the same; they're 12 centimeters in diameter and a millimeter thick, and they have an opaque top and a reflective bottom. Such is the Tao of the disc.
As you can see in Figure 1-1, however, the structure of a mass-produced disc isn't a single piece of plastic. It's made up of a number of layers, each of which has something special to add to the mix:
A label: Commercially manufactured discs you buy in the store have screen-printed labels; these graphics are created from layers of ink applied one on top of the other (like that Metallica T-shirt you may be wearing). What's that, you say? You don't have $2,000 or so to spend on a special CD screen printer? (Come to think of it, neither do I!) In that case, do what I do and use your inkjet or laser printer to create a fancy paper label, complete with the graphics and text you choose (more on this topic in Chapter 14).
TIPS
"Do I really need a label?" To be honest, no. A disc you've recorded works fine without one. However, if you've ever dug through a 6-inch stack of unlabeled CDs to find that Andy Williams Greatest Hits disc you burned a month ago for Aunt Harriet, I guarantee that you will understand. If you don't need a professional look and you're not into appearances, just use a CD-marking pen and scribble a quick title on top. Most recordable discs have blank lines printed on them for just this purpose. You can pick up one of these handy pens at any office supply store, but make sure that you buy a pen designed especially for marking CDs.
Opaque plastic: You need something to protect the top of the disc. I suppose that you could use steel, but then a disc would weigh two pounds and cost much more. Therefore, the manufacturer adds a layer of scratch-resistant plastic.
Aluminum film: Mass-produced CDs use a thin layer of aluminum that's covered with microscopic indentations called pits. These pits are arranged in a single, tiny groove that spirals around the disc, just like the groove on one of those antique record albums. (If something works, why mess with it?) However, the groove on a CD starts at the center and spirals to the outside of the disc, so it goes in the opposite direction.
More plastic: Again, all that shiny aluminum has to be protected - however, in this case, the plastic must be crystal-clear (for reasons that soon become apparent), so the manufacturer adds another layer. Here's a hint about why this layer is clear: It has to do with the passage of laser light. As I mention earlier in this chapter, this yummy sandwich is a cross-section of a commercial CD produced at a factory - the discs you record are different in one important way, which I cover in a minute.
DVDs are similar to CDs in construction, but, as I remind you from time to time, commercially produced DVDs can be double-sided (so you can flip them to watch the second half of a really long film, like Das Boot or Gone with the Wind). Therefore, they may not always have a label side, in which case th0e sides are marked around the spindle hole.
How Is Data Recorded on CDs and DVDs?
Consider just how audio, video, and computer files are stored on CDs and DVDs. Although these three types of information are different, they're stored in the same way: digitally. But what does that word really mean?
Programmers, technotypes, and hardware jockeys use the word digital when they're talking about binary, the language used by computers around the world. Unlike the imprecise languages spoken and written by mere humans, binary data is built from only two values - 0 (zero) and 1, which are often referred to as Off and On, respectively shown in Figure 1-2. (In fact, a computer is only a huge collection of switches, but that's another story.) Therefore, computer files, movies, and digital music are long lines of 0s (zeros) and 1s. If you sat next to a light switch for 100 years and flipped it off and on in the proper sequence, you would have the visual version of a digital song from a CD (and a bad headache along with incredibly sore fingers).
Now that you're privy to the binary master plan, you can see how the absence and presence of light perfectly represents binary data - a room is either dark or bright. The geniuses who developed CD and DVD technology took this concept one step further! They had the great idea of using a laser beam to read the binary data stored on a disc, and that's where those pits in the aluminum layer that I mention in the preceding section take center stage.
Figure 1-3 shows how the binary data is read: When the laser beam hits a pit on the surface of the disc, the beam scatters, so most of it isn't reflected back: hence, darkness, which in this case stands for a 0 (zero) in binary data. If the laser beam hits one of the flat surfaces - they're called lands, by the way - the beam is reflected cleanly back, and the drive senses that reflected light. (Think of a 1 in binary.) And, ladies and gentlemen, that is why the business end of a disc shines like a mirror; the rainbow effect is caused by the microscopic groove that runs across the surface. Naturally, this process happens very fast (I talk about speed in Chapter 2), but that's really all there is to it.
Essentially, DVD technology works the same way - with a difference or two. A DVD-ROM can hold the approximate equivalent of seven CDs, and Figure 1-4 shows how: The pits on a DVD-ROM are much smaller and are packed closer together on the surface of the disc, and the drive uses a much more powerful laser beam to read them. DVD can also have multiple reflective layers. (That's the reason that data can be stored on both sides.)
TECHNICAL STUFF
Believe it or not, the DVD specification standard provides for double-sided DVD-ROM discs that have two layers on each side, for more than 27 CDs' worth of storage space on a single DVD-ROM! However, these discs are so hard to manufacture that they're on the endangered species list, and I've never actually seen one.
It's All in the Dye
Consider the structure of recordable discs, which includes both recordable CDs and recordable DVDs. Remember the aluminum film that I mention in the section "Always Begin with a Definition" earlier in this chapter? Sounds permanent, doesn't it? Indeed it is, which is why you can't use commercially manufactured discs to record your own data; your recorder has to be able to create the equivalent of pits and lands in some other way. (Not even Bill Gates has a CD-R manufacturing plant in his house.)
Figure 1-5 shows the answer as well as a really bad pun. The CD-R (short for compact disc recordable), which can be recorded once, uses a layer of green or blue reactive dye under a smooth reflective surface of either aluminum or gold. The groove is still there, but until the disc has been recorded, the disc is perfectly empty. This dye permanently melts or darkens when hit by a laser beam of a certain frequency, which results in a pit. (As you find out later in the chapter, a number of DVD recordable formats are currently on the market, but things work the same.)
"Hang on, Mark - wouldn't the beam from my regular read-only CD-ROM or DVD-ROM drive cause problems?" Good question, but the designers of recordable CD and DVD drives have you covered. The laser beam that is used to read a disc is far less powerful than the beam used to record one. Therefore, when the beam from the laser in your CD-ROM or DVD-ROM drive hits one of these dark spots, the beam is swallowed like an apple pie at a state fair, so it acts just like a pit in a mass-produced CD. In fact, your read-only drive is completely fooled ... it can't tell the difference.
TECHNICAL STUFF
The inside of your CD or DVD recorder sounds like it's getting a little crowded with all these different laser beams, but it's really not. A recorder has a beam that can be set at two levels: a lower power setting that can read a disc and a higher setting to record it. Slick, eh?
A CD-RW, which is short for compact disc rewriteable, is another story. (Get ready: You're going to love this description. It honestly sounds like something out of Star Trek - the original series, not any of those later failures that don't have Captain Kirk.) Here goes: Both rewriteable CDs and DVDs use a "phase change recording process" using a "crystalline layer with amorphous properties" rather than a dye layer. Didn't I tell you? It sounds like something Spock would say! You can promptly forget that stuff because nobody but an engineer cares, and no one gives a test afterward.
Anyway, although the crystalline layer starts out clear, the correct type of laser beam can change it to opaque, creating - you guessed it - a pit. When you're ready to erase the disk, that same beam of laser light resets the crystalline layer to clear again, and you're ready to record all over again. Talk about recycling!
Behind the Curtain: Inside CD-RW and DVD Drives
Before I delve into the depths of your hardware, I want to make one thing perfectly clear: You do not have to read this section! In fact, if raising the hood on your car and just looking at the engine gives you a headache, I encourage you to skip this section entirely. It's definitely not necessary to know what makes your drive tick.
Still here? I didn't scare you away? Good! If you're like me, and cool machinery like your recorder fascinates you, stick with me and read on! In this section, I show you the interior guts of your CD-RW or DVD recorder.
The motor
Because pits are arranged around the entire disc, something has to turn it - in this case, an efficient, high-speed electric motor. (No coal or gas here, Bucko.) The motor turns a spindle, which holds the disc by the hole in the center - yet another similarity to vinyl record albums!
The laser stuff
A CD-ROM or DVD-ROM drive has a laser read head, and a recorder has a read head that can be set to variable power levels. When you read a disc, the laser beam is focused through a lens upward toward the surface of the disc; if the beam is reflected by a land, the light travels through a prism to an optical pickup. In turn, the pickup yells to your computer (in effect) "Hey, I just passed a land back there, so add a 1 to the file."
When a drive is recording, the laser beam is switched to its higher power; the beam simply travels up to the surface of the disc and creates a pit by discoloring or melting the dye layer in one tiny spot.
Continues...
Excerpted from CD & DVD Recording For Dummies by Mark L. Chambers Excerpted by permission.
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