PC Hardware in a Nutshell, 3rd Edition

Buffer Underrun Protection

In the past, anyone who used a CD writer sometimes made coasters, the common term for a ruined CD-R blank. Although packet writing and UDF effectively eliminated coasters, packet-writing software was useless for batch-mode tasks, such as duplicating CDs. Those tasks demanded premastering software, which unfortunately was by no means immune to generating coasters.

Originally, CD premastering was inherently an isochronous (time-dependent) process because data had to be delivered to the write head in a continuous stream from the time the write began until it completed. If that stream was interrupted long enough for the data stored in the writer’s buffer to be exhausted—an accident called a buffer underrun—the blank was ruined. Buffer underruns were particularly common with IDE/ATAPI CD writers, although they were by no means rare even on SCSI burners.

Sanyo effectively made buffer underruns a thing of the past by developing a technology called BURN-Proof (Buffer UnderRuN-Proof) and licensing it to CD writer makers. In simple terms, BURN-Proof turns off the writing LASER when it runs out of data to write (duh), and then, when data is again available, restarts the burn exactly where it left off. In effect, BURN-Proof converts CD writing from an isochronous process to an asynchronous one.

BURN-Proof works by constantly monitoring the status of the CD writer’s buffer to detect a potential buffer underrun condition. If the amount of buffered data falls to a ...