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Writing Multiple

CD-R and CD-RW are essentially the best tools for those who want to burn CDs.  Of the two, CD-RW drives are becoming more popular, because you can reuse the CDs.  Even though rewritable drives and media are typically more expensive than CD-R (but not by much), the convenience of rewritability and the lower long-term media expense offset the initial cost.

But one of the CD-RW's major points, writing in multiple sessions, is also one of its major problems - not from a technology standpoint but from a user's standpoint.  Users are often confused about the process of multi-session writing, and the software that comes with the CD-RW drives is often obscure in this matter.  It's hard to know what options to use in order to write to a CD in multiple sessions, because issues such as closing and linking sessions and closing the disk come into play.  When you consider that you can use several recording formats, the confusion multiplies.

In this article I'll go over how to record in multiple sessions using Adaptec's Easy CD Creator, by far, the software most commonly included with CD-RW drives.

Multiple-session Recording Facts
To get the idea of multi-session recording straight, you must know the various ways of recording to CDs.  The three most common are disk-at-once, track-at-once, and packet writing.

Disk-at-once records the entire disk at one time. Another words, the content is prepared on the hard drive and the laser records everything you specify to the CD from start to finish.  Disk-at-once closes the disk after recording is completed; this method can't be used for multi-session recording.

Track-at-once records one track at a time, then turns off the recording laser until the next track is ready to record.  Until recently, track-at-once recording has automatically set the gap between tracks at 2 seconds.  This may be more or less than you want if you're recording an audio CD.  Newer CD-R and CD-RW drives support variable-gap track-at-once, which allows you to set the gap from a fraction of a second up to several seconds, as long as your recording software also supports this feature.

Packet writing lets you record small amounts of data (or packets) to a CD incrementally.  When Easy CD Creator offers you the option of creating a CD that will act as a hard drive - giving you the ability to save, copy, or move files to it - the software is choosing packet-writing mode.  The CD-RW drive must support packet writing; not all do.

The next thing to know is the way a CD drive reads CDs.  A large number of audio CD players won't read CD-RW disks at all.  You can write audio tracks to a CD-RW in multiple sessions, but the audio CD player won't be able to read them (and play them) until the entire disk - not just the individual session - is closed.  In other words, you must compile your entire collection of audio CD tracks for the CD and then record them either in disk-at-once format, which closes the disk automatically, or track by track, leaving the disk open (and unplayable) until the final track is recorded and the disk is closed.  The big benefit of working with CD-RW media is that you can erase all the data on the CD and reuse the disk - even after it's been closed.

Note that newer CD-Writing programs, such as Adaptec's Easy CD Creator 4.0, let you reuse the CD-R media by blocking off the existing data so that it's inaccessible and then making the remainder of the CD-R writable.

This answers one of the questions for people recording their first CDs:  if you've been trying to record a few songs onto a CD, then play them in your car, then add a few more later, it simply won't work.  Your car CD won't read anything until you close the disk, and once you've done so, you can't add more sessions.  And even if you could, the system would see only the first session anyway.  You can, however, play an unclosed audio CD on most recent computer CD-ROM drives, so if you plan to listen from your PC, go right ahead.

A closed CD session has three areas.  The lead-in contains the table of contents (TOC), the program area contains the data, and the lead-out tells the CD reader that the session is closed.  The lead-in and lead-out consume several megabytes of space, so the more sessions you add, the more space on the CD these regions take up (remember that each session needs a lead-in and a lead-out).  The lead-in and lead-out are written when a session is closed, which means that for single-session CD burning, all of this happens in the single recording, and for multi-session burning, they are written as each session is closed.

The lead-in contains one other important piece of information:  the address of the next writable area of the disk, if there is such an area.  If the disk is closed, there isn't.  This information is crucial for multi-session recording to work.

Writing Multiple Sessions to CD-RW Disks

Multi-session recording is the process of adding data to a CD in increments.  Each track is recorded separately and then linked, so the CD drive can read the tracks as if they were recorded in one session.  Linking is also a frequent source of user confusion, and understanding what it means can help a great deal with making CDs that work properly.

When the lead-in is written to the CD, it contains both the TOC and information about the next writable address on the CD (as mentioned above).  This data allows you to link sessions.  Each session has its own file system, and the file system created for a new session can contain references to the addresses of the files from a previous session.  Through linking, multiple sessions of a CD can recognize one another, and the files will appear as one long list to any CD-ROM drive capable of reading CD-RW media (which includes all recent models).

In the past, the only way to guarantee linked sessions was to start a new session as soon as you closed the current one,  Today's CD-authoring software, however, lets you link the sessions by simply adding files to an existing rewritable CD, as long as the CD itself has not been closed.

Multiple Sessions with Easy CD Creator
The entire process of creating CDs with Adaptec's software now makes sense.  Now's the time to go through the process of setting up a disk for multi-session recording.

When you want to add more data at a later point, put the CD in the drive and open Easy CD Creator.  When the wizard appears, tell it that you want to create a data CD.  The wizard will automatically import the existing sessions from the CD into the Data CD Layout area.  Go through the wizard's steps, add your new files, and then have the wizard create the CD.  It will add the new files, close the session, and leave the disk open for you to do this all over again.

You don't actually have to use the wizard to do all this; you can open the Data CD Layout from its saved location on your hard drive, and then add files by dragging and dropping from the top half of the Easy CD Creator window and then choosing 
File | Create CD.

Writing multiple sessions to a CD-RW disk is simple with the help of Easy CD Creator.

Step 1:  Insert a blank CD-R or CD-RW

Step 2:  Easy CD Creator Wizard

Step 3:  Select files to record onto the CD

Step 4:  Create CD

Step 5:  The CD Layout Properties

Step 6:  Close Session and Leave Disk Open
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