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CD-R drives have two speeds that matter: the record speed and the read speed, both expressed as multiples of the 150-KBps speed of the original CD-ROM drives. The record speed, which is listed first, is always equal to or slower than the read speed. For example, a CD-R drive with a specification of 8×24× would burn at 8× and read at 24×.

CD-RW

For all their usefulness, CD-R drives have disappeared from the market. Notice that I didn’t say CD-R discs have disappeared; more CD-R discs are burned now than ever before. Just as CD-R drives could both burn CD-R discs and read CD-ROMs, a newer type of drive called CD-rewritable (CD-RW) took over the burning market from CD-R drives. Although this drive has its own type of CD-RW discs, it also can burn to CD-R discs, which are much cheaper.

CD-RW technology enables you not only to burn a disc, but to burn over existing data on a CD-RW disc. This is not something you need for every disc—for example, I create CD-R archives of my completed books to store the text and graphics for posterity—this is data I want to access later, but do not need to modify. While I’m working on content for the CD that accompanies this book, however, I may decide to delete an item; I couldn’t do that with a CD-R. The CD-RW format, on the other hand, essentially takes CD-media to the functional equivalent of a 650-MB floppy disk. Once again, CD-RW discs look exactly like CD-ROM discs with the exception of a colored bottom side. Figure 13-22 shows all three formats.

Figure 13-22 CD-ROM, CD-R, and CD-RW discs

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CAUTION You can rewrite CD-RW discs a limited number of times. The number varies according to the source, but expect a maximum life of about 1000 rewrites, although in real life you’ll get considerably fewer.

A CD-RW drive works by using a laser to heat an amorphous (noncrystalline) substance that, when cooled, slowly becomes crystalline. The crystalline areas are reflective, whereas the amorphous areas are not. Because both CD-R and CD-RW drives require a powerful laser, making a drive that could burn CD-Rs and CD-RWs was a simple process, and plain CD-R drives disappeared almost overnight. Why buy a CD-R drive when a comparably priced CD-RW drive could burn both CD-R and CD-RW discs?

CD-RW drive specs have three multiplier values. The first shows the CD-R write speed, the second shows the CD-RW rewrite speed, and the third shows the read speed. Write, rewrite, and read speeds vary tremendously among the various brands of CD-RW drives; here are just a few representative samples: 8×4×32×, 12×10×32×, and 48×24×48×.

One of the goals with the introduction of CD-RWs was the idea of making a CD-RW act like a hard drive so you could simply drag a file onto the CD-RW (or CD-R) and just as easily drag it off again. This goal was difficult for two reasons: first, the different file formats made on-the-fly conversion risky. Second, CD-RWs don’t store data exactly the same way as hard drives and would quickly wear out if data were copied in the same manner.

Two developments, UDF and packet writing, enable you to treat a CD-RW just like a hard drive—with a few gotchas. The not-so-new kid in town with CD-media file formats is the universal data format (UDF). UDF is a replacement for ISO-9660 and all of its various extensions, resulting in a single file format that any drive and operating system can read. UDF has taken over the DVD world (all movie DVDs use this format) and is poised to also become the CD-media file format in the near future. UDF handles very large files and is excellent for all rewritable CD-media. UDF has been available for quite a while, but until Windows Vista came out, no version of Windows could write to UDF-formatted discs. They could read the discs, but if you wanted to write to them in Windows you had to use one of a number of third-party UDF tools such as Roxio’s DirectCD and Nero’s InCD. UDF also supports a feature called Mount Rainier—better known as packet writing