Mac Forum / General / General / September 2006

If you have disk problems, using this alerts you to this or any other
problems and prevents a wasted disc.  Or multiple wasted disks.  Takes a
few minutes though.

Simulation mode works by going through the motions of writing the CD,
but without activating the laser to actually burn the CD.

It was important back in the dark ages before Buffer Underrun protection
and when CD-R media was more expensive. With early CD writers, the
computer had to be able to sustain the data transfer rate required for
the speed chosen when burning the CD, i.e. not let the CD writer run out
of data. If there was even a momentary delay in delivering data which
allowed the CD writer's buffer to empty, then it immediately stopped
writing and reported a failure, resulting in a useless CD.

Using Simulation mode was a good was to ensure the burn would work
(assuming no changed circumstances on the computer in a subsequent real
burn), because it would report the same error if there was a buffer
underrun, but without wasting a CD in the process.

Nowadays, buffer underrun protection allows the CD writer to pause and
resume, which is OK for 99% of cases but it might still be useful to
turn off buffer underrun protection if doing something like burning a
master CD for professional replication (which must have no underrun
errors or the duplication process might fail, which could be very
expensive). In this case, simulation mode can be used to ensure that the
original CD will burn without wasting a blank.