3.4 Seamless Link
Seamless Link protects the disc writing process against the effects of buffer underrun.
Today, many advances in CD writing technology are not only related to speed and to ensuring optimal
write operations on nearly all media, but also to writing integrity.
However, users with older systems may still be presented with an occasional buffer underrun error
message. Though a less frequent error for users of new computer systems, buffer underrun still is an
annoying problem as the recordable media will be irretrievably lost. For both users of new and older
systems, Philips Seamless Link offers an excellent solution for minimizing this disastrous effect of
buffer underrun.
About Buffer Underrun
Buffer underrun can occur when the users’ computer cannot supply a steady and uninterrupted flow of
data from the data source, typically a CD-ROM or hard disk drive, to the memory buffer of the CD or
DVD writer drive.
If this transfer of data, to the drive memory, is interrupted long enough to empty the write buffer in the
drive, then the writing process stops and the disc is ruined. Buffer underrun occurs most frequently
when users are writing in either Track-at-Once (TAO) or Disc-at-Once (DAO) mode.
Possible causes for buffer underrun:
· Insufficient processing power (low speed CPU, insufficient RAM size, no DMA support)
· System configuration not optimal (DMA switched off)
· Too much user interaction during writing (starting or running additional applications, thermal
recalibration of older hard disk types)
· Insufficient performance of the source drive (CD-ROM, hard disk, network drive)
· Scratched or dirty source media (source drive needs multiple retries to read the data successfully)
The solution? Seamless Link from Philips
Seamless Link, the Philips solution, detects the clues of an imminent buffer underrun ahead of time. It
pauses the writing in a controlled way, and restarts the writing when the danger of the buffer underrun
is gone.
Seamless Link technology, however, does not prevent the occurance of buffer underruns. Seamless
Link only acts to prevent buffer underruns from wasting a disc, it is not a speed or quality optimization
algorithm. For speed and quality optimization it is always better to try and remove the cause for the
buffer underruns.
How Seamless Link Works
Seamless Link constantly monitors the writer buffer level. If this level drops below a threshold value,
the writing process is stopped in a controlled way. This means that the data stream from the buffer to
the disc is halted, and it allows the buffer to be filled up again.
The exact location on the disc, where the write operation was stopped, is stored in the drive’s internal
memory. In the meantime, the buffer level is continuously monitored and as soon as the buffer is full
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