DirectCD for Macintosh – A Packet Writing Primer (abridged from Roxio’s website)
If you have a CD-RW drive, or use CD-Rs for backing up individual files, DirectCD could be a useful tool for you. DirectCD uses packet writing, a relatively recent method for recording CDs (as opposed to Toast and Easy CD Creator, which use a mode called Track-At-Once [TAO]). Since small packets of data can be written at a time, it is possible to mount a CD-R or CD-R/W disc on the desktop, and copy to it as you would a hard drive. This can be very convenient and it allows a lot more flexibility than the Track-At-Once (TAO) mode. However, packet-written CDs don’t have the near universal support that traditional CD-ROMs written by Toast have.
Packet writing involves writing small pieces of data, or packets, much like a hard drive. Unlike TAO, which takes 21MB for the first session as overhead, and 13MB for each additional session, packet writing has a much smaller overhead. This makes it a lot more flexible.
While regular CD-ROMs are usually mastered in either the Macintosh filesystem (HFS) or ISO 9660 formats, packet writing uses a newer standard, called Universal Disk Format (UDF). UDF is the key to understanding packet writing. DirectCD for Macintosh supports Sequential writing, as it is required for the more common (and less expensive) CD-R media. However, it does not support Spared writing; when you use CD-RW media it is written just like CD-R media (space doesn’t get erased and reused). This means that the only advantage to rewritable media is that the whole disc can be erased and reused. The PC version of DirectCD uses the Spared method for rewritable media, which means that the Macintosh version can’t write to it (although such discs can be read). While CD-RW discs are written sequentially by DirectCD for Mac, it is still possible to move files, throw files away, and even empty the Trash. The bytes that were written to the disc are still there, but the references to them are gone. This is how a hard drive works, with the exception that the space on a hard drive can be reused.
As you might have guessed, using UDF instead of the standard HFS filesystem means that you need something for your Mac, or your friend’s Mac, or your friend’s PC to be able to recognize the disc. Roxio has a free extension for both Macintosh and PC computers to let discs be recognized by systems without DirectCD, called the UDF Reader. Perhaps you have noticed that Apple has already included something called “UDF Volume Access.” This won’t help your Mac recognize all UDF CDs, as it only supports the Normal, not the Spared or Sequential, flavor.
Unfortunately, without DirectCD, a disc that is still open (able to be written to) won’t be mountable even with the UDF Reader. CD-ROM drives don’t know how to handle open discs, and a CD recorder (which knows how to handle open discs) needs a special driver (like the one in DirectCD) to know how to handle Sequentially written discs. To be read on a normal CD-ROM drive the disc needs to be closed (and the UDF Reader installed). But once closed, a Sequentially written disc cannot be written to again (unless totally erased, of course). Making things even more complicated, the CD-RW discs written by DirectCD for Windows (which uses the Spared flavor of writing) are always”closed,” can be added to (as well as rewritten) on PCs, and are readable without DirectCD being installed (although you would still need the Roxio UDF Reader).
DirectCD for Windows, with CD-R media (Sequentially written), closes to ISO 9660 plus Joliet (a Microsoft extension that allows up to 64 character filenames) while preserving the UDF information. With the UDF Reader installed, a Mac user will be able to see up to the normal 31 character limit. If sharing longer filenames (e.g. Java files) be careful about this limit! Without the UDF Reader, only the basic “8.3” filenames will be readable, although Thomas Tempelmann has created a free extension that enables a Macintosh to see Joliet filenames up to the 31-character limit.
While DirectCD for Macintosh doesn’t support writing the Spared flavor, it can write to CD-RW media just fine. To erase and start fresh requires Toast, as DirectCD for Macintosh currently doesn’t have that capability. In Toast, select “Disc Info…” from the “Format” menu to find the Erase button. This process takes a while, but can run in the background.
Another complication to note is that although CD-RW media is supported by DirectCD and Toast, there are still a lot of CD-ROM drives that don’t support it. CD-RW media is physically different from CD-R media and is outside of the CD specifications. So a drive needs to be designed to read it. Often such drives are marked as “MultiRead,” however, some drives support it without mentioning it. The only way to be sure is to try it.
The ability to treat a recordable CD like a hard drive is DirectCD’s most obvious advantage. Avoiding the overhead of writing a standard TAO CD is a less obvious, yet still important advantage. The first session written in TAO takes 21MB of additional space, and each additional session takes 13 MB more! The more universal file system (UDF) is another advantage. However, UDF is also a disadvantage because of compatibility issues – the need for software support and closed discs when such discs are distributed to others. For personal use, and sharing files back and forth with someone who also has a CD recorder, it works well.
There are some specific problems with the current version of DirectCD for Macintosh. One is an issue in an older version of Mac OS where space would be used up merely by having the disc inserted! This was worked-around in later versions of DirectCD (and Apple fixed the problem in later systems), you can find the latest update on Roxio’s support site. More troublesome is that later versions of Mac OS (8.5 and higher) write to volumes nearly every time a window is opened or closed to update the list of open windows, resulting in frequent and unnecessary updates to the disc.