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Buffer under run can occur when the users’ PC or a host PC cannot supply a steady and uninterrupted flow
of data from the data source, typically a CD ROM or HDD, to the internal DRAM buffer of the CD writer
(writer buffer) (Fig. 1). If this transfer of data to the drive writer buffer is interrupted, then the buffer is not
kept full (Fig. 2). If the interuption is long enough, the "writer buffer" gets empty, the writing process stops
and the disc is ruined (Fig. 3). Buffer under run occurs most frequently when users are writing to a CD-R or
CD-RW disc in either Track-at-Once (TAO) or Disc-at-Once (DAO) mode.
The causes of BUR have been numerous and are related to the PC system, the system configuration or set up,
and the CD writer itself. Most sources of BUR have been reduced in newer PC systems (with faster CPUs
and HDDs with transparent Thermal Recalibration), and by improvements in both
CD writer and the application software.
ABOUT BUFFER UNDER RUN (BUR)
Fig. 1, Typical CD writing process: The data that needs to be written on the disc is transferred from the
source over the system bus, and is put into the DRAM buffer of the CD writer. From this buffer, the data
is put onto a disc in the writing process.
Fig. 2, Typical CD writing process: Short interruptions in the transfer of the data over the IDE bus will cause
the writer buffer level to drop.
CD writer
Internal DRAM buffer, “writer buffer”
compensates for
short interruptions
in the data stream
CD writer
If the data stream is interrupted, the speed at which
the data is sent to the writer is lower than the speed
at which the data is written to the CD
=> the level of the writer buffer
will drop.
After the interruption, the writer
buffer level will rise again
Fig. 3, Typical CD writing process: Buffer under run occurs and results in writing failure, disc is ruined.
CD writer
Writer buffer level drops to 0%
· No more data available to write to the CD
· Writing stops => BUR
BUR occurs when this
stream is interrupted
Several primary sources of BUR are:
· Insufficient PC processing power (low speed CPU, DRAM size, no DMA support)
· System configuration not optimal (DMA switched off)
· Too much user interaction during CD writing (launching or running additional applications)
· Insufficient performance of the source drive (CD ROM or HDD in user system or network)
· Insufficient performance from the mastering software, espec. at higher recording speeds
· Insufficient performance of the writer (not enough internal memory or buffer…)
· Scratched or dirty media (source drive needs multiple retries to successfully read)
Seamless Link, the Philips solution, is a BUR management solution that is “on board” the drive and prevents
a lost disc when a buffer under run occurs during TAO or DAO writing. Detecting the clues of a imminent
BUR ahead of time, Seamless Link pauses the writing in a controlled way, and restarts the writing when the
danger of the BUR is gone. The result is effective with most older systems, when proper system set-up is done,
and Seamless Link works transparently with most writing application software.
The primary benefits to users of both new and older PC systems are:
· The Philips "intelligent drive" pro actively manages the consequences of a BUR during CD writing
· The solution allows users greater ability to launch and run other applications..., or surf the web,
while burning a CD.
Although Seamless Link is an excellent tool for managing the impact of BUR when it occurs, Seamless Link
does not improve writing quality.
For improvements in writng quality, refer to the Philips' Thermo-Balanced Writing (TBW) white paper.
BUR MANAGEMENT FROM PHILIPS!
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