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6-3-2] Do I want to do packet writing?




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This article is from the CD-Recordable FAQ, by Andy McFadden (fadden@fadden.com) with numerous contributions by others.

6-3-2] Do I want to do packet writing?

(2003/01/13)

It depends. If your primary interests are writing audio CDs, duplicating
CD-ROMs (for backups, right?), or creating CD-ROMs full of files that you
can give to others, packet writing won't help you much.

Discs written by programs like Roxio DirectCD aren't usable in a CD-ROM
reader until they're finalized. Finalized discs are in ISO-9660 format,
but it's ISO-9660 Level 3, which not all operating systems can interpret
(Win9x and WinNT can, with appropriate "redirectors" installed).

On the other hand, if you want to be able to add small amounts of data over
time, it may be extremely useful. You can read the unfinalized discs on
your system, so the data isn't inaccessible; it just can't be accessed on
other systems that aren't also set up to do packet writing. You can
overwrite files on CD-R media (the old data is still there, but the newer
directory entry points to the new file), something that was very costly
with multisession writes. And, of course, the risk of a buffer underrun
is almost nonexistent.

Most backup software (by which I mean backing up your system, not "backing
up" the latest game) uses packet writing. This can affect your ability
to read backups from some operating systems, notably MS-DOS. See section
(4-52).

As with CD-RW, it doesn't hurt to buy a recorder that supports it, but
you're probably not missing much if you have one without it. (As of the
year 2002, nearly all new recorders support both.)


Now, a reality check: sometimes packet-written discs "go funny". This could
be because the CD-RW media is wearing out, or because the computer locked
up when some data was pending but not yet written, or because the software
has bugs. Whatever the case, DO NOT write your only copy of valuable data
to a packet-written disc and keep adding stuff to it. If you do, there
is a good chance you will be making a contribution to the people listed
in section (6-2-6).

The format that has proven the least reliable of all CD formats is
packet-written CD-RW media (which almost always uses fixed-length packets).
Writing to a CD-R with variable-length packets is a big step up, especially
since nothing is ever really erased from a CD-R. If it's important data,
write it to a CD-R (with packet writing or, better yet, conventional
disc-at-once recording) and then close the disc and don't write to it again.

Having had our reality check, I can point out that a HUGE number of people
use packet writing every day, for the most part without even realizing it,
and relatively few suffer for doing so. It's important to understand the
risks and act appropriately.


 

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