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Hi again,
When I access large amounts of data from a DVD or CD, the drive
makes a rapid clunking sound, almost like some hard drives make rapid
clicking sounds. I know this is normal because all my disk drives, including
the one in my Xbox make this noise. If optical disk drives are anything like
hard drives, I assume this noise is the laser rapidly jumping back and
forward. I am just wondering why it does this. When I tell my PC to copy an
entire DVD or CD to the hard drive, since it ultimately has to read all the
data on the disk, why doesn't the laser just follow the spiral track and
slowly move outwards, a bit like a record player needle would? I've also
noticed that it only "clunks" when it is changing the file that it is
reading, for example; if it is copying 20 files per second, it will make the
noise twice every second, but if it is copying very large files, it will
only make the noise once it is finished and moves onto the next one (if that
makes any sense). While I'm asking this, why does a hard drive do the same
thing?

Thanks for any answers,
a confused newbie!

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"Mushroom" <> wrote in message
news:cfigqu$4ur$...
> When I access large amounts of data from a DVD or CD,
the drive
> makes a rapid clunking sound, almost like some hard drives make
rapid
> clicking sounds. I know this is normal because all my disk drives,
including
> the one in my Xbox make this noise. If optical disk drives are
anything like
> hard drives, I assume this noise is the laser rapidly jumping back
and
> forward. I am just wondering why it does this. When I tell my PC to
copy an
> entire DVD or CD to the hard drive, since it ultimately has to read
all the
> data on the disk, why doesn't the laser just follow the spiral track
and
> slowly move outwards, a bit like a record player needle would? I've
also
> noticed that it only "clunks" when it is changing the file that it
is
> reading, for example; if it is copying 20 files per second, it will
make the
> noise twice every second, but if it is copying very large files, it
will
> only make the noise once it is finished and moves onto the next one
(if that
> makes any sense). While I'm asking this, why does a hard drive do
the same
> thing?

If a file is stored in discontiguous clusters on the HDD, the
read/write head needs to move around the disk surface to access
different fragments of the file.

I think this would also apply _if_ a file was also broken into
multiple parts on an optical disk. However, if the optical disk
was made through the press process or an image burning, all data
should be in contiguous blocks. I don't know if packet writing
techniques (e.g. DirectCD, UDF, etc.) can generate file
fragments just like those on HDDs.

In addition to file fragments, the order in which the files are read
and the presence of large might also affect the frequency of the laser
movement.



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