"Cliff Top" writes:

There is always a limit switch/home position the laser sled returns to to
start reading. The start of the spiral track will be directly under the
laser at that point. At the end of the disc there is ~2mins of 'stop code'
so that when the laser finds itself here, it will know it must trigger
'stop' mode.

Note that the "start" of the spiral track is about 1.6 um wide. The
limit switch gets you in the ball park.

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CD writers are a little different since they can access an earlier porion of
the disc for power calibration tests.

AW

"Brad" wrote in message
...
Hi,

Thanks to everyone for pointing me in the right direction with regards
to the "initial" track position (inside) when you first insert a data CD.

Another very important question: Is there a physical "stop" that
stops the head (the head moves toward the center of the CD and "hits"
a physical stop) at that "initial" track position, or is this done
by "seeking" that "initial" track?

Thanks in advance, Brad

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