11.10 Burning CDs

11.10 Burning CDs

The following sections condense our experience in burning a lot of CDs in various environments.

11.10.1 General CD Burning Guidelines

The process of burning CDs can be smooth and reliable or a complete nightmare. Which it is depends on the entire system you use to burn CDs—processor, memory, operating system, configuration settings, background processes, hard disk type and fragmentation level, source CD-ROM drive and the source CD itself, CD-R(W) drive, firmware revision, application software, and the blank discs themselves. In short, the process of burning CDs is a black art rather than a science.

That's less true now than it was even a couple of years ago, because systems are faster and CD burners are better. But it still pays to keep in mind that what counts is not just the CD burner or the blanks, but the entire system. Once you have the system working reliably, making even a minor change to one element can break it. For example, we once added an apparently innocuous Windows NT service to our main CD-R burning system. Suddenly, a system that was formerly rock-solid for burning CDs was no longer reliable. Removing the service cured the problem.

On a properly configured system, you can burn hundreds of CDs uneventfully. On a marginal system, even the slightest problem or anomaly can result in a ruined CD blank, called a "coaster." Making an occasional coaster is less aggravating now that blanks cost $0.50 each instead of $20 each, but it still wastes at least five minutes or so. So, no matter how good your system is, use the following guidelines to burn CDs reliably:

Regardless of the interface or operating system, take the following steps before recording a CD:
- Disable screensavers, schedulers, antivirus utilities, and any other software or service that may interrupt the recording process. In particular, if your PC is configured to answer phone or fax calls, disable that for the duration of the burning session.
- When recording from a disk image (writing the source data to the hard drive as an intermediate step, rather than doing a direct CD-to-CD copy), defragment the disk drive before starting the burn.
- If your PC is on a network and is configured to share its disk or printer, disable sharing before attempting to burn a CD. If another user accesses your disk or printer while the CD is burning, the burn may fail.
In the past, conventional wisdom was that making high-quality reproductions of audio CDs required that both source drive and CD burner be SCSI. That's no longer true, as some recent ATAPI CD-ROM drives are suitable as source drives for high-quality audio duping, but the ATAPI CD-ROM drives common in most PCs of 1998 or earlier are likely not suitable source drives. If your CD-ROM drive is in the latter category, you can still do high-quality audio dupes by using your CD burner as both source drive and destination drive. Doing so requires that your CD copy utility support disc-to-image copying, whereby your burner reads the source CD, writes an image of that CD to your hard drive, and then uses that image as the source.
If the data to be copied resides on a network drive, copy it to the local hard drive before attempting to burn the disc. Writing data from a network drive frequently yields a coaster, even on a 100BaseT network. Note that this caution applies only to writing CD-R discs, which is a synchronous (timing-critical) operation. We have frequently written CD-RW discs from data located on a network drive. Recording CD-RW discs in packet-writing mode is an asynchronous operation, so network delays have no effect on the integrity of the copy.

11.10.2 Burning On-the-Fly Versus Burning Image Files

Broadly speaking, there are three ways to burn a CD-R disc, whether the source data is another CD or a random collection of files on your hard disk.

Burning on-the-fly: With this method, data is streamed from the source CD or hard drive, formatting and error correction data is added in real-time, and the resulting data stream is burned to the CD. The advantages of on-the-fly burning are that it is faster than other methods and that it requires no extra disk space. The drawback is that on-the-fly burning is the method most likely to create coasters. Most recent systems are fast enough to dupe audio or data CDs on-the-fly successfully, but you may have problems if you attempt to write hundreds or thousands of relatively small files to a CD, for example, if you use your CD writer to back up your hard disk.
Burning true image files: This method uses a two-step process. Data to be written to the CD is first read and processed to add formatting and error correction data. That formatted data is then written out to the hard disk as an ISO image file, which is an exact binary representation of the data as it will be written to the CD. The drawbacks to using true image files are that it takes longer and that you must have enough free disk space to accommodate the image file, which can be 1 GB or more when you are copying audio data to an 80-minute blank. However, burning a true image file is by far the most reliable method, particularly on older, slower systems and those that use an older model CD writer.
Burning virtual image files: This method is similar to using true image files, with the exception that an actual image file is not written to the hard disk. Instead, a virtual image file is created, which contains pointers to the locations of the files to be written to the CD. Because formatting, adding error correction, and all other pre-processing is done before the actual burn starts, using a virtual image file is more reliable than burning on the fly. Conversely, because the files to be written must be retrieved from random locations on the hard disk during the burn, using a virtual image file is less reliable than using a true image file. Using virtual image files is slower than burning on-the-fly but faster than using true image files.

The best method to use depends on the capabilities of your system, your CD writer, and your software, as well as the type of data you want to burn to CD. On-the-fly burns usually work well for duping audio or data CDs, and (assuming that you have enough free disk space) using a true image file is best for doing backups and similar operations that require writing many small files to disc. As always, the best way to judge is to try each method and use the fastest one that works reliably for you.

If you are building a new system or installing a new hard disk on a CD writer system, we recommend creating a dedicated hard disk partition to be used as a "staging area" for ISO image files. This partition needn't be large—a gigabyte or so is sufficient—but it should be on your fastest hard disk if there's a choice (and certainly on a hard disk that is on a different channel than the CD writer).

Configure your burning software to write the ISO image file to the dedicated partition. After you complete each burn, you can delete the ISO image file or move it elsewhere, freeing up the partition for the next burn. We've never had a problem just deleting the old ISO image file, but some belt-and-suspenders folks we know do a quick format of the partition each time to ensure the ISO image file is written sequentially to the partition.

11.10.3 Choosing the Optimum Burn Speed for Your Drive and Media

Don't assume that you can use your CD writer's fastest speed, even if your burning software tests a disc and claims that it is writable at the highest speed. In general, burning at higher speeds is less reliable than burning at lower speeds, both because faster burning is more likely to generate errors while writing, particularly with marginal discs, and because the CD writer's buffer, whatever its size, empties faster at higher burning speeds. For example, when writing at 12X (1,800 KB/s), a 512 KB buffer stores only about a quarter of a second's worth of data. Any interruption in the data stream longer than that generates a coaster (unless, of course, your drive supports BURN-Proof or a similar technology). Larger buffers and lower write speeds minimize the chance of that happening.

But slow equals reliable is by no means a universal truth. Burning at a slower speed is not always more reliable. For example, we have one 8X CD writer that writes most discs reliably at 8X, some discs reliably at 4X, and very few discs reliably at 2X or 1X. The optimal burning speed depends on numerous factors, particularly the combination of drive, firmware revision, and disc.

In general, when we start with a new batch of media on a given CD writer, we first attempt burns at the highest rated speed of the drive, regardless of the speed for which the media is certified. For example, we have a spindle of no-name 4X certified media that works without problems at 8X on all three of our Plextor 8X burners, both SCSI and IDE. Those same discs, however, generate about 10% coasters in our Smart & Friendly 4X burner when burned at 4X or 1X, but nearly 50% coasters when burned at 2X. Go figure.

Also note that the type of data you are burning and your staging method can make a difference. For example, we have some no-name 8X certified discs that work fine for on-the-fly copies of data or audio CDs at 8X. But when we attempt to use those discs to do an 8X on-the-fly backup of our hard disk, coasters generally result. If we instead use a true image file as the source, the backup runs fine at 8X to those discs. Conversely, if we back up to Kodak 8X certified discs, both the on-the-fly and the ISO image backup work reliably. It shouldn't make a difference—8X is 8X—but it does.

As always, the best solution is to test in your own environment.

Are Test Burns Worth Doing?

A test burn performs the entire CD writing process, but without actually writing the CD. In theory, a test burn lets you do a rehearsal without wasting a blank disc if something turns out to be wrong with the setup. The idea of test burns is left over from the Bad Old Days when a blank disc cost $25 or $50. At that price, taking pains to avoid burning coasters was worthwhile, so everyone did test burns.

The problem with test burns, though, is that they aren't a very good predictor of success during an actual burn. Oh, if a test burn fails, you can be pretty certain that a real burn would also have failed; but if a test burn succeeds, that's no guarantee that the real burn will also succeed. It is quite possible to do a successful test burn immediately followed by a failed actual burn, because the test burn doesn't test the actual writing process, which is by far the touchiest aspect of the whole process. A successful test followed by a failed burn is particularly common on systems with marginal power supplies, which are adequate during the testing phase, but cannot provide sufficient power when the CD writer laser is running at full burning power.

Nowadays, a test burn is just a good way to waste time. All CD writer software supports doing test burns, but we suggest you don't bother doing them. The only real way to test is to burn a CD. If it succeeds, you're done and you can get on with your life. If it fails, you're out half a buck or so, but you've gotten some useful information.

11.10.4 Overburning

Overburning simply means writing more data to a CD-R blank than it is nominally designed to store, allowing you to fit more music or data on a standard CD-R disc. This is possible because most CD-R blanks contain more than the necessary number of writable sectors. For example, a 74-minute blank, which must have at least 333,000 sectors to yield 74 minutes of recording time, may actually contain 340,000 sectors, which allows it to record about 75.5 minutes. The number of "extra" sectors varies widely between different brands of CD-R blanks. Some contain only a few extra sectors, while others contain enough extra sectors to allow recording up to 76, 77, or even 78 minutes on a nominal 74-minute blank.

To overburn successfully, the media, the CD recorder, and the software must all support overburning. If your software supports overburning, it is probably not configured to use it by default. You'll likely need to enable overburning manually, possibly for each disc you want to overburn.

In the days before 80-minute blanks became widely available, overburning was a popular way to defeat the ad hoc copy protection used by some game CD makers, who simply pressed CDs that contained more sectors than would fit on a standard 74-minute CD. The widespread availability of overburning-capable software and 80-minute blanks has almost eliminated the use of this means of copy protection.

Do not overburn unless you are certain your CD writer supports it. Although we have never encountered the problem, we have numerous reports of CD writers that did not support overburning being physically damaged by attempting it. Even if your software allows overburning, do not assume that means it is safe to use overburning on your writer. Verify with the manufacturer that your writer supports overburning.

If for some reason you need to burn CDs larger than 650 MB/74 minutes, keep the following issues in mind:

If your CD writer and/or CD mastering/duplication program does not support overburning 74-minute discs, you may be able to use 80-minute discs instead. Although 80-minute discs are less reliable than 74-minute discs, they are probably more reliable than overburned 74-minute discs.

You can overburn 80-minute CDs, but it's probably not worth bothering. In the first place, most 80-minute blanks contain few extra sectors, often only enough for an extra minute or less. More important, even CD-ROM drives and CD players that can read 80-minute CDs may choke on overburned 80-minute CDs.

Some CD writers and software support overburning 74-minute discs but do not support 80-minute discs, some support 80-minute discs but not overburning, some support both, and some support neither. If software is the limiting factor, check the maker's web site. The most recent versions of most CD-R software have been upgraded to support 80-minute discs.
Some CD writers can be upgraded to support 80-minute media by installing a firmware update. Others are physically incapable of writing more than 74 minutes or slightly more.
The media types most suitable for overburning, which is to say those with the greatest number of extra sectors, are often otherwise undesirable. If you buy some of these oversized discs for overburning, use them only when you need to overburn something.
Most CD writers that do support overburning do so only in Disc-at-Once (DAO) mode, which limits you to duplicating an audio or data CD (as opposed to premastering the data, as for example when you select a group of files and folders to copy). Some CD mastering software overcomes this problem by allowing you to create an ISO image of the data on your hard disk as a preliminary step, and then burning that image to the CD.
Although it may seem possible to determine the maximum length of an overburn exactly, that is not the case. For example, a CD-R disc utility may report that a blank contains 351,000 sectors, which can be converted mathematically to a burn time of 78:00:00. But in reality, limitations in your CD writer hardware or firmware will likely place a shorter absolute limit on the actual burn.
Even if your CD burner and software support overburning, don't be surprised to see some pretty horrifying error messages during an overburn, such as Fatal write error, Track following error, or Write emergency. In fact, it's pretty common while doing a long overburn to have the software lock up at or just before the Writing Table of Contents phase. It may appear that you've made a coaster, but it's worth checking to see if the disc is readable. It often is, although by all rights it seems that it shouldn't be.
Even if your CD burner and software support overburning and the process appears to complete normally, you may find that the material past the standard 74-minute length is degraded. Audio tracks may have various artifacts, including hisses, pops, and drop-outs. Data files may be corrupted. The more extensive the overburn, the more likely such problems are to occur.
Overburning is a (rather dubious) art rather than a science. Actually, the same can be said in general for burning CDs, but this is particularly true when overburning. Just because you succeed once in overburning a disc doesn't mean that you'll succeed the next time, even with an identical disc and the same data.
Some CD-ROM drives and CD players, particularly older models, cannot handle overburned and/or 80-minute discs. The usual symptom is that the drive or player refuses to accept the CD, simply ejecting it as soon as you insert it. Sometimes, a drive or player reads the first 650 MB/74 minutes and then simply stops reading in the midst of an audio track or file. In general, any time you burn a CD larger than 650 MB/74 minutes by whatever method, be aware that read problems may result.

All of that said, our general advice is as follows:

Stick to standard 74-minute CDs if at all possible, and don't try to record more than they are designed to hold. Otherwise, expect problems.
If you absolutely, positively need to record more than 74 minutes on a CD, use an 80-minute blank in a CD writer designed to support it.
If for some reason you must overburn a 74-minute blank, first make sure your CD burner supports overburning. Keep the overburn as short as possible, and test the resulting disc in the actual drive that will be used to read it before you assume that the disc will be readable.