1. Chapter VI, Digital Storage: Lesson IV CD Formats and File Systems

2. An important step in the creation of a CD-R is an up-front decision about how the file system of the CD will be organized. For optical-disc creation, the term "file system" does not refer to a file management structure with directories and subdirectories, as might mistakenly be assumed.
Rather, it refers to strategies and processes by which the information is named, organized, and retrieved from the disc. The two most common file system types are: ISO-9660
Joliet

3. File Systems: ISO-9660
The ISO-9660 file system ("ISO" stands for "International Standards Organization") is probably the ideal system for disc that need to be distributed to a variety of users.
It is flexible enough to operate on:
DOS systems
Windows systems
UNIX
Macintosh
OS/2
Later LINUX Systems
ISO-9660 requires that file and directory names be 8 characters in length with 3-character extensions. It limits a disc to 8 levels of subdirectories.

4. File Systems: Joliet The Joliet file system allows
names up to 64 characters in
length, including spaces
(which are ignored by ISO-9660).
When burning file-system
information to a CD-R, Joliet
also records an (8+3) version
of all file names, so that DOS
systems and early versions of
Windows will still have access
to the files. Joliet file system CD-Rs only work on a PC platform. If any sort of cross-platform distribution is anticipated, it's best to avoid Joliet. But if long file names are important for archiving and rapid recognition, Joliet may be a preferable option.

5. File Naming:
Joliet:
Being limited by ISO-9660 to an 8+3 naming convention sometimes isn't practical.
Consider, for example, a series of files named:
Invoices_Oct2001.doc
Invoices_Nov2001.doc
Invoices_Dec2001.doc
When archived as ISO-9660 file system data, the names would be truncated to:
Invoic~1.doc
Invoic~2.doc
Invoic~3.doc
This makes the quick location of November invoices rather cumbersome.

6. Other questions that need be considered for selecting between Joliet and ISO-9660 include:
Am I archiving a document
with external links
(e.g., a PowerPoint show
that imports charts or video)?
Some links to other files
may be lost if long file names
are truncated by ISO-9660.
Do I need these documents
sorted by date? ISO-9660 will
reorganize files into alphabetical
order; Joliet retains the order
you designate.
Will this disc be used on other computers? ISO-9660 is your safest bet for near-universal playback on other platforms.

7. Types of Data
As Lesson 3 demonstrated with audio CDs, CD-Rs don't have to treat all data equally. Several options exist for different data types, as well as for combinations of data types on a single disc.
These options include:
CD-ROM XA
Video CDs
CD EXTRA ("hybrid")

8. Types of Data: CD-ROM XA
CD-ROM XA ("Extended Architecture") is a modification of CD-ROM standards to provide better video and audio playback functionality from a disc. XA is a combination of
2 disc writing modes:
Mode 1, which is best for standard data that requires disc space for error correction information.
Mode 2, which takes little space for error correction and allows video and audio data to be interleaved for high-quality playback.
CD-ROM XA is an ideal option for multimedia presentations on disc.

9. Types of Data: Video CDs
Video CDs, as well as Photo CDs, are a subset of CD-ROM XA. The XA format brings out the best of videos. Since videos require no error detection or correction code, and since Mode 2 eliminates the need for a full pre-load of images, the video starts faster and plays smoother.

10. Types of Data: CD EXTRA ("hybrid")
CD Extra is another variation on the CD-ROM XA format. It turns a disc into a combination Audio CD that will operate in standard audio disc players, and a data CD for computer CD-ROM drives.
The music industry has begun to move forward on the mass distribution of hybrid discs, marketing audio CDs with bonus music videos to be viewed on home computer systems. A variant of CD EXTRA, called "Mixed Mode," also allows hybrid discs, but places audio information in later sessions.

11. Single session vs. Multi-sessions
On a CD-R, a "session" is a recorded segment of any data type. A session doesn't have to be recorded all at once, but once your writing software tells a disc to "close a session," the information can be played back on other computers, in different CD-ROM drives. If you close a session, you may very well be closing off the entire disc to any additional data writing.

12. Single sessions are most commonly used for audio-only CDs
Single sessions are most commonly used for audio-only CDs. This is because most audio CD players will only read a disc's first session; all subsequent sessions are ignored. Again, this does not mean that all audio has to be recorded in a single sitting.
Audio CD creation software (built-in for most CD writing software packages) will prompt a user to decide whether a session should be closed, or should remain open. Sessions left open can be appended with additional audio files. However, the disc cannot be played in standard audio players or CD-ROM drives until the session has finally been "closed."

13. Multi-session discs, first introduced for Photo CDs that required the addition of new images after a first session was closed, permit a user to continue appending files in second, third, and additional sessions. The disc's directory is continually updated to reflect all files from all sessions of the disc.
Each new session requires 9 MB of space for the creation of new header information.

14. Initially, the advantage of multi-session discs was the ability for multiple users to view a disc (the first session had been closed) and to add more data to the same disc (a second and subsequent sessions could be added). Thanks to the advent of Extended Architecture (XA), those benefits were expanded to allow the inclusion of different types of data in different disc sessions.

15. Most newer CD-ROM drives recognize multi-session discs.
Since multi-sessions discs use the ISO-9660 file system, they are subject to the same benefits and limitations discussed earlier in this lesson.

16. On-The Fly vs. Image Recording
Most CD-R writing software packages provide the option to write a disk directly from another CD-ROM drive ("on-the-fly" recording), or to first create a complete image of the data to be copied to disc ("disc-from-image recording") on the hard drive.
There are plusses and minuses to
each approach, depending on the
disc-creator's needs.

17. On-the-fly disc creation has the benefit of speed
On-the-fly disc creation has the benefit of speed. The writing software creates a virtual directory of the files to be copied to disc, and then proceeds with the copy file-by-file. The virtual directory is flexible: the user can add or subtract files
before writing the session. Little
time is lost, since all that's being
altered are the names of files the
software plans to find and copy.
The downside of on-the-fly disc copying has more to do with hardware limitation than it has to do with software. CD writers can experience "buffer underruns," when too little information is transferred to the CD writer to keep the data stream intact. For older units, on-the-fly disc writing may result in numerous errors, eradicating the benefit of any time savings.

18. Disc-from-image CD writing is literally what it says:
The creation of a CD-R from a pre-created hard-disk image composed entirely, and only, of the information that will be transferred. This takes a little more time, but it reduces
the possibility of buffer underrun. An additional benefit of copying from
a disc image surfaces when multiple,
identical discs need to be created.
Once the image has been created
on the hard drive, subsequent
burnings are just as fast as
on-the-fly copies. The choice between on-the-fly and disc-from-image CD-R creation must take into account the need for speed, for accuracy, and free hard-drive space for image storage.