CD burning — the speed you need

It wasn’t long ago that CD burners were rare, and now almost every PC has at least a CD or even a DVD burner. This is not surprising since CD burner prices have crashed through $100, a mere fraction of what you would have expected to pay back in the late 1990s. Burning a CD is relatively easy, but the details of working with CDs and DVDs can be confusing. That’s why we are starting a new column specifically geared towards CDs and DVDs. To get the ball rolling, this month we will cover the issue of burning speed.

CD ratings

Over the years, the most common question I have been asked is “What speed should I use to burn CDs?”. Before answering this, it is important to understand a little about how CDs are rated.

CD burners have three different functions. They read data like a normal CD drive, and they can burn data to CD-R or CD-RW discs. When rating a CD burner, manufacturers use the maximum speed of each task. This is measured in terms of the original standard, i.e., the speed at which a normal audio CD plays. Hence, 2x is twice as fast as the original, 4x is four times as fast, and so on. Reading data is frequently the fastest function, and burning a CD-RW the slowest. As such, a model rated at 48x32x16x has a maximum reading speed of 48 times the standard (abbreviated as 48x), a CD-R burning speed of 32x and a CD-RW burning speed of 16x.

Now to a key part of the rating system — the maximum speed applies only to the outer area of the CD. The speed is significantly slower around the centre of the disc. If you have ever ripped an audio CD, you would have noticed that the first (inner-most) tracks take longer to transfer than the outer tracks.

Here’s a tricky question. If you have a 700MB (80-minute) CD and burn it at 40x, how long will it take (assuming the data fills the entire 700MB)? If you have never done it, your might guess an answer of two minutes (80 divided by 40x = 2 minutes). In reality, it is more likely to take 3 to 4 minutes. The first reason for this anomaly is that, as mentioned above, the drive reaches its maximum speed only at outer portion of the disc. The data at the centre is written substantially below 40x.

The next factor is that the burning process is a little more complex than just writing your files to plastic. Even before the data is written, a table of contents (TOC) is burned to the CD. On faster drives, this takes about 30-40 seconds, regardless of whether you select a 16x, 20x or 40x burning speed. The upshot? Even before the files are written, you have already used over half a minute — and maybe more.

After the TOC and data files are laid down, the CD is finalised — another process that can affect the total burn time. There are other steps in the burning process that chew up more time — such as file system generation — but for the sake of brevity, we will leave them for another time.

Speed vs. time

To see how burning times vary, you can try some of your own experiments using different burning speeds. All you need is a stop watch and some suitably-sized files.

If you are not the scientific type, I have some results using 20x and 40x burning speed on the same burner. At 100MB there is no difference in burn times. Even at 700MB, the absolute maximum time you will save is a relatively minor 52 seconds.

For those people who love the details, a Plextor 40x12x40x burner was used with Easy CD Creator 6. Data were burned onto Imation CD-R media (rated to 48x) with a single data file in zip format and burned using the Disc-at-once (closed) option.

And the answer is…

Now to the nitty gritty — what burn speed should you use? The assumptions are: you have a new-ish PC (at least 1GHz and an Ultra ATA66 hard drive or better), and the computer is not suffering performance issues. Under these conditions you should burn at about 16x-20x.

Obviously, if your CD burner has a rated maximum below 16x-20x, use its maximum. Likewise, slower PCs should burn CDs at lower speeds.

The reason for this choice is simple: you get little or no time benefit for burn speeds above 20x, but there is an increased chance of buffer underruns (a subject we will come back to in future columns) and other issues such as possible problems.

An important point to keep in mind is that the above discussion relates to different speeds on the same CD burner. Consider a situation where you are creating an identical CD on two different burners: one has a maximum rating of 16x, and the other is a 40x burner set to run at 16x. At first glance, it would seem both these burners will take the same time to create a full CD. In fact, the 40x burner will be substantially faster. As mentioned earlier, the outside track is used for the maximum speed rating, but this also means that nearer the centre of the CD the 40x burner — even when set to 16x — will still burn the CD more quickly than the 16x speed burner.