Frequently Asked Questions About CD-R and CD-RW Discs

Please contact Media Sciences if your questions are not answered on these pages.

Even after a successful recording, a CD-R disc may not readable. The drive does not recognize it. Does this indicate a defective unrecorded disc?

Probably not. This is not an unusual problem, especially when a desktop computer is used for recording. All compact discs have a common structure, beginning with lead-in, then the program area, and finally lead-out. Information that is recorded in the program area cannot be accessed unless proper lead-in and lead-out areas are present. One or both of these are usually missing or corrupted when a drive will not recognize a recorded CD-R. Various parts of the recording system can cause such a flaw.

Lead-in is critical because it contains the table of contents (TOC) of the disc. The TOC contains ATime locations for the beginning and end of every logical track. Read drives will not recognize the disc if they cannot read the TOC. An unwise choice of recording method can lead to TOC problems because some methods do not write the TOC until the end of a recording when the session is finalized, or closed.

Disc-at-once recording is the safest recording method, since the entire disc is written in one uninterrupted operation. Lead-in is recorded first, then the program area, and finally lead-out. Data flow to the write laser is continuous, and opportunities for errors are minimized. Buffer underrun errors are normally reported by the recording software if power management, screen savers, or other resident operations fatally preempt the flow of information to the writer.

Track-at-once is an alternate method of single session recording. The program area is written first, then laser power is lowered to the read level while the optical head seeks to the lead-in area and writes lead-in, then power is again reduced, the head seeks to lead-out, and finally the lead-out area is recorded. Three distinct recordings must be flawlessly completed, creating many possibilities of handshaking conflicts between the host, recording software, SCSI bus, and the writer. A flawed TOC can result from bugs in this handshaking process that actually occur, as witnessed by the frequent release of firmware revisions for writers, new SCSI drivers, and recording software updates.

Multisession recording is another potential cause of read failures. Lead-in and lead-out areas for each session are written only when it is closed. The TOC contains track locations for only that session unless recording software supports linked multisession. The disc remains open for future recording sessions, and will not be recognized by a CD-ROM drive. Finalization of the disc records information for all sessions in the very last TOC, using information stored in a Program Memory Area (PMA) of the CD-R, allowing all sessions to be accessed by a multisession-capable read drive. CD-ROM drives that lack this capability can only read the first session. Multisession recording has a large number of possibilities for error, any of which can cause the written disc to be unreadable.

Although CD-R disc defects can create problems, these are usually found in the program area, and will not cause the read drive to fail to recognize the recorded disc. Problems resulting in recognition failure are more likely caused by the writer, SCSI bus, recording software, or host system. Operator error may even be responsible if the wrong recording software option box is checked. Pinpointing such problems can be frustrating because they are often intermittent. Implementation of dependable recording practices are preferred to lengthy efforts that attempt to precisely identify the elusive cause.

Avoid latest-and-greatest versions of software and hardware drivers that may contain fatal bugs that have not yet been discovered or fixed. Verify that the recording software version is known to be stable, and utilize disc-at-once recording when possible. Confirm that the SCSI driver is known to be stable and properly configured for CD-R recording according to recommendations of the manufacturer. Perform simulated recording tests at all drive speeds and at full disc capacity, preferably writing many small files. Close all applications other than those used for recording. Carefully explore the operating system and disable all terminate-and-stay-resident programs (TSR's) such as anti-virus programs, screen savers, alarms, and reminders. Disable all advanced power management (APM) located in the BIOS, operating system, and other programs such as SCSI utilities. Avoid network connections, even if the node is not logged on.

Many other considerations too numerous to outline here are essential to reliable recording. Suppliers of professional systems should have identified and implemented all such requirements in their fully tested systems. Desktop users often have limited resources, and can experience unpredictable failures. Proven recording systems from reliable vendors are recommended when reliability and longevity are highly important. Multitasking desktop systems may not satisfy such demands.