How It Works: Optical Drives

by Reads (44,731)

by Dustin Sklavos

The “How it Works” series has gone on for six exciting, adrenaline-pumping, action packed parts so far, explaining the nitty gritty of all the stuff that makes your laptop perform. You should by this point have a clear understanding of where all the bottlenecks and boondoggles in your laptop are and be able to make some informed decisions.

Or can you?

While we’ve covered the vast majority of the internals thus far, it’s important to keep in mind that you still have to connect things to your laptop. There are other utilities you may use it for outside of the odd game of Minesweeper (a personal favorite) or taking notes, because let’s face it: If you were just going to use your laptop for that you might as well just save your money and buy an Eee PC, since it does that stuff just fine.

But now we’re going to discuss a part of your laptop that I’m sure you take for granted: your optical drive.

How It Works: Optical Drives

Most of you probably call it the DVD burner or CD writer or DVD drive, but the best all-encompassing technical term for these drives is “optical drive.” Why? Because that’s how they work, and all of them are variations on a basic theme: a motor spins the disc in the drive super fast while a laser attached to a servo reads data off of it. This is why these drives tend to be pretty loud and draw a lot of power: a whole lot of stuff is moving.

If you think back to last article when I talked about hard drives, you’ll see similar concepts: a circular disc containing data which is read by a moving head. But while hard drives can hit transfer speeds close to 100MB per second (especially on the desktop), optical drives seldom hit anywhere near that. Data on optical discs is less dense, and the mechanisms for reading it are different.

Optical drives, similar to hard drives, also have a small amount of built in memory, but because data on a disc is nowhere near as dense (or numerous), cache is usually very small and not terribly important for you to know.

Anatomy of a Disc

In order to understand how the optical drive works, you need to know how an optical disc works. This is pretty simple. The disc is basically three layers: the big plastic disc part is on the bottom, a reflective surface is in the middle, and then the top part of the disc is where the art or label is, and this part actually protects the data itself. The data is kept in microscopic pits in the reflective surface. This is why scratching the disc itself isn’t catastrophic.

Scratches still aren’t good for it though, because the laser used to read the disc is tuned very precisely, and if the disc is damaged, the wrong scratch or hair may refract or block the beam and make the data difficult to read.

That reflective layer sandwiched between the plastic part and the label part is also one reason why you want to use soft pens or markers when writing the label on your writeable disc: the label layer is basically protecting the reflective surface which contains the data.


Now that you know the fundamentals, it’s all just variations on a theme. CDs, DVDs, HD-DVDs, and Blu-rays are all basically just different methods of tuning the same core technology to cram more capacity onto the disc. A finer laser results in being able to increase data density on the disc itself.

We’ll get to writeable, rewriteable, and dual layer stuff in a second. There are four (well, three still active) basic formats.

CD (Compact Disc) is the granddaddy of them all. Featuring the lowest capacity (topping out at 700MB), CDs remain the cheapest and easiest to produce since the data is not that dense and therefore easier to read.

DVD (Digital Versatile Disc) is the descendant. DVDs top out at 8.54GB in dual layer while a single layer DVD can hold 4.7GB. The laser used to read DVDs is a bit finer, and the higher capacity resulting made them ideal for video and data backup tasks.

Blu-ray and its defeated opponent HD-DVD (High Definition DVD) are where a bifurcation in the format occurred. You were probably aware of this. Blu-ray is so named because it uses a finer, blue-violet laser for reading data. HD-DVD uses a similar blue laser. The main differences between the two had to do with their total capacity (Blu-ray can do 25GB in a single layer and 50GB in a dual layer while HD-DVD could only do 15GB per layer) and their ease of manufacturing (HD-DVDs could be manufactured with minor changes at regular DVD factories while Blu-ray required a substantially larger overhaul).

Let’s be clear for a second here: for data archival purposes Blu-ray does indeed just kick HD-DVD around, all over town. More capacity is just plain king there. For doing high definition movies, though, the difference in capacity isn’t really a major one. High definition movies, encoded properly, don’t need much more space than is provided on a garden variety dual layer DVD.

The HD-DVD and Blu-ray battle wasn’t decided by the public, it was decided largely by back room politics, though in fairness, while HD-DVD was a superior movie format for consumers (not for its quality, but for its features, lack of region coding, and consistency), Blu-ray is superior for computer usage. If we’re moving into the future, the higher capacity of Blu-ray does make it more ideal.

Oh, and in case you were wondering why you can’t just write a CD with a finer laser, part of each of these specifications requires a different laser for reading them and so on. The various formats physically can’t work any other way.

Layer Change

So this is all very exciting, but what the heck does all that single and dual layer stuff mean? Dual layer discs have two reflective layers sandwiched between the label side and plastic side instead of one. The first of these layers is semi-transparent, so the laser can change its focal length and read through it to the next layer.

If you have an older DVD player at home, you may notice movies pause at a certain point for maybe a second. This is the result of the layer change on the disc, and I’ve actually seen this occur every so often with high definition movies as well. Computer optical drives tend to be much more tolerant of layer changes and have the benefit of system memory to buffer them so the transition can appear seamless.


Okay, so now that we’ve established our types, let’s hit the sub-types. These are specified by a suffix attached to the disc type. For future reference, while movies are just referred to as “Blu-ray,” in computer terms, Blu-ray discs are referred to as “BD,” similar to CD. The etymology should be obvious. Moving on …

“-ROM” stands for “Read Only Memory” and indicates a disc that cannot be written to, only read.

“-R” stands for “Recordable.” This is a disc that can be written to once. This is applicable to all formats, but there’s a bifurcation here that needs to be discussed later on.

“-RW” stands for “Re-writeable.” This disc can be written to, erased, and written to again. This is again applicable to all formats, but has the same bifurcation that “-R” does. For Blu-ray, this is referred to as “-RE.” Why they didn’t just stick with “-RW” I’ll never know, but whatever.

“-RAM” stands for “Random Access Memory” and is the weird one out, appearing only for DVDs. DVD-RAM discs are basically designed to be usable like the floppy discs of old, and because of their flexibility this way, they are very popular in camcorders that write directly to discs. The flipside is that these bad boys tend to be pretty expensive, and write speeds on them are often slower than their “-RW” counterparts. It also tends to be less compatible than the other formats.

“DL” is an extra suffix that stands for “Dual Layer.” This currently only applies to DVDs; dual layer Blu-ray discs are also available, but there’s no initial distinction made, the packaging will just specify the capacity.

Now, I’m sure many of you have seen “DVD+R” or “DVD+RW.” Basically, the + and – versions of these formats occur only in DVD, and have their pro’s and con’s. All DVD writers on the market these days can write to either one, and most drives can read either one fine. “+” format discs are usually a little faster and a little cheaper. “-” format discs, on the other hand, feature one major benefit: they sport excellent compatibility. Generally DVD+R discs will work fine in most drives that can read DVDs, but when they don’t, a DVD-R almost always will.

There was briefly a generation of DVD players early on in the format’s lifetime that deliberately didn’t read writeable media, probably because the manufacturers expected us to only use it for piracy. DVD-R discs, on the other hand, tend to do an excellent job of fooling these players and will run quite happily in most anything. It’s for this reason that as a media major I use DVD-Rs almost exclusively.

Drive and Disc Speeds

As far as read speeds go, these numbers have become largely irrelevant. Read speed for any given drive is invariably “fast enough.”

Speed ratings for optical drives are measured pretty crudely, basically in multiples. You’ve seen “52x” CD-ROM drives, and the CD-Rs at the store may be rated for “16x.” The basic problem is that it requires some mathematics to actually yield a theoretical bandwidth speed, so at the end of the day it’s basically just “52x is faster than 48x but it really doesn’t matter anyhow.” Unless you’ve just gotta have that extra 1MB a second, in which case this series just isn’t going to be able to provide you with the kind of help you need.

But there is, however, one important place where these speeds matter, and that’s write speeds. When you try to write an optical disc, usually the computer will give you an option of how fast you want to write it. The key here is that writeable or re-writeable optical discs also specify a safe range of speeds where you can reliably write to them, and some are specced for “High Speed.”

Almost all CD-Rs generally max out write speeds at this point, but just about everything else has some variation. If you’re not sure how fast your drive can write, then keep this in mind: your drive can always slow down to take advantage of slower media.

It also bears mentioning that re-writeable discs are almost always substantially slower than regular writeable media.

Region Coding and Piracy

I’d be remiss not to mention this, and it won’t matter to the vast majority of readers. Optical drives are basically coded to a specific region in compliance with DVD digital rights management. These region codes matter solely to DVD, HD-DVD, and Blu-ray movies.

DVDs have the most restrictive regional lockouts, and sport six different region codes (along with the most preferable one, region 0, which means the disc can be played anywhere). The most important ones to know are region 1 (USA and Canada), region 2 (Western Europe), and region 3 (Southeast Asia and Japan). Of course, if you’re an aggressive DVD importer, there are ways around regional lockouts. Unfortunately, the computer methods almost always involve software of questionable legality in the United States where we’re based, so I can’t really talk about those.

Blu-ray is substantially less restrictive, with just three region codes: A covers the Americas, India, Southeast Asia, and Japan; B covers Europe and Australia; and C covers Russia and China.

Finally, lamentably, HD-DVD had no restrictions this way, so naturally it went by the wayside.

Now, piracy: don’t do it kids. Most optical media for games has some kind of protection preventing you from making proper copies of the discs themselves. Almost all DVDs have this, so don’t get all excited like “oh, I’m gonna copy movies off Netflix.” First, if you’re the type who rents, copies, and sends back, you’re a tool and you’re part of the problem. I hate digital rights management with a passion as it really only punishes honest consumers, but honestly, ignoring all the politics involved … if you like a movie, just buy the thing. You could make a case for CDs and Blu-ray movies being horrendously overpriced, but DVDs? Come on. I just got The Terminator for $3.99. It’s affordable.

Lightscribe and Labelflash

I don’t want to go into too much detail with these, but it’s basically technology that allows you to use the optical drive itself to burn monochrome labels into the top of media designed for this purpose. This process tends to be time consuming (can be a half hour or longer per disc), but can also look pretty cool. You’ll need to buy the proper media to do it (labeled “Lightscribe” or “Labelflash”), and you’ll need to make sure the drive can support it. Mercifully, notebooks do tend to advertise these pretty aggressively.

Lightscribe is the more popular of these two technologies, and parties almost exclusively on the HP side of town. If your drive can do Lightscribe, there should be a sticker on the notebook telling you just that. Failing that, the drive itself is often labeled (at least on mine).

Media Quirks

Really, it’s the writing part that makes these things so freaking complicated. Basically, don’t buy cheap writeable media.

Let me explain. All “-R”s and “-RW”s are not created equal, and some are of substantially higher quality than others. Unfortunately, recommending brands can get a bit tricky because some drives will just write happily to about anything while other drives can get really picky. I have a DVD writer at home that used to be just peachy with Memorex media, but now produces coasters on anything but TDK.

I will say that you should avoid the cheapo ones at all costs. In house brands like Dynex, Staples, and GQ are going to produce poor quality discs that may not last long and will certainly have difficulty reading in some drives.

Of course, the unicorn in the room is Taiyo Yuden, generally regarded as the best brand of writeable media. These are almost impossible to find in retail and require special ordering, but if you simply must have the best, these are where you want to go.

Re-writeable media is also kind of flaky. It tends to read and write slower than regular media, but more importantly, after a few writes and rewrites these can turn into coasters, so buyer beware.


This is one of those situations where I can’t offer any clear recommendations: buy the drive you need. Notebooks generally only give you this option when they’re being custom ordered, so you’re pretty much stuck with whatever they give you. This usually isn’t a problem.

I wish I could distill this article for you as I’ve done in articles past, but the problem here is that optical drives are largely governed by aggravating minutiae. If I tried to distill things I’d wind up writing the article all over again, and you and I both would rather go play Mass Effect, so there’s that.

Coming Up: Screens

If there were one thing I really wish people knew off the bat, resolution is it. But what about glossy and matte? All this and more about the biggest battery hog in your laptop, next time!



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