O
Original TankGirl
Guest
Detectors and DVD's
> "Will-Lee-Cue" wrote in message:
> Close but no cigar.
Here's the real story.
> CD's that are written by computers use a lazer to etch a pit into the
> surface of the media.
> Comerical CD's are stamped much like the old vinyl records (not burned
with
> a lazer).
Only commercial CD's have "pits".
CD'S written by computers burn a dark spot on the media. They don't "etch a
pit".
> Re-writeable CD's (CD_RW) heat a spot with a lazer and a magnet is used to
> pull a dimple into that spot while it is hot. (happens very very fast)
> Once the spot cools the dimple stays put and will be read as if it were a
> pit created by a CD-R lazer.
CD_RW's can be altered not because "a dimple is pulled", but because they
have numerous layers, and a new recording burns dark spots on a different
layer.
Neither CD's nor CD_RW's are affected by magnets, unless you drop a
magnet on the data side and scratch the surface.
> "Larry Gadbois" <[email protected]> wrote in message
> news:[email protected]...
> > Passing a powerful magnet over a commercial DVD or CD will not damage
it.
> > The digital information is stored on these disks by a stamping process
> > using a master disk. The master creates small pits that do not reflect
the
> > laser beam back to the sensor in the player mechanism. The interruption
> > of the reflected beam is detected and converted to a digital bit stream.
> >
> > DVD+R, DVD-R, DVD+RW,CD+R,CD-R,CD+RW (home recordable types) work on a
> > different principle. When the disk is being written, a laser is used to
> > heat a small spot on the rotating disk. The recording head extends the
> > full radius of the disk. As the spot is heated, the data is recorded at
> > the heated spot by rearranging the magnetic particles on the magnetic
> > reflective coating. The spot instantly cools as the disk spins and the
new
> > magnetic pattern is imprinted in the coating. The magnetic pattern
causes
> > a change in laser beam reflection when played, and the digital
information
> > is detected.
> >
> > A very powerful magnet may be able to change the imprinting on a some
home
> > recordable disks. The laser beam used during recording heats the coating
> > to the Curie point at which the media can easily be imprinted as it
cools.
> > Without heating the coating, the magnetic particles are not easily
> > rearranged.
> >
> > All metal detectors radiate an electro-magnetic field from the coil at
one
> > or more radio frequencies. Because of the long wavelengths and low power
> > involved, a metal detector will not damage any CD or DVD. A hard drive
> > would not be damaged or altered by exposing it to a metal detector
either.
> > The case and circuit design of a hard drive does a good job of shield it
> > from electrical or magnetic damage.
> >
> >
> >
> > "Von Fourche" <[email protected]> wrote in message
> > news:[email protected]...
> >>
> >>
> >> Ok, if I take a powerful magnet and swipe it across a DVD the DVD
will
> >> probably get messed up.
> >>
> >> I just wondering: will a metal detector do the same? If I take my
> >> DFX,
> >> turn it on, and then put a DVD under the coil will the DVD get
> >> erased/screwed up?
> >>
> >> Also, what about computer hard drives? Can a metal detector mess
them
> >> up too?
> >>
> >> Strange questions I know. I'm just wondering!
> >>
> >> Thanks!
> >>
> >>
> >
> >
>
>
> "Will-Lee-Cue" wrote in message:
> Close but no cigar.
Here's the real story.
> CD's that are written by computers use a lazer to etch a pit into the
> surface of the media.
> Comerical CD's are stamped much like the old vinyl records (not burned
with
> a lazer).
Only commercial CD's have "pits".
CD'S written by computers burn a dark spot on the media. They don't "etch a
pit".
> Re-writeable CD's (CD_RW) heat a spot with a lazer and a magnet is used to
> pull a dimple into that spot while it is hot. (happens very very fast)
> Once the spot cools the dimple stays put and will be read as if it were a
> pit created by a CD-R lazer.
CD_RW's can be altered not because "a dimple is pulled", but because they
have numerous layers, and a new recording burns dark spots on a different
layer.
Neither CD's nor CD_RW's are affected by magnets, unless you drop a
magnet on the data side and scratch the surface.
> "Larry Gadbois" <[email protected]> wrote in message
> news:[email protected]...
> > Passing a powerful magnet over a commercial DVD or CD will not damage
it.
> > The digital information is stored on these disks by a stamping process
> > using a master disk. The master creates small pits that do not reflect
the
> > laser beam back to the sensor in the player mechanism. The interruption
> > of the reflected beam is detected and converted to a digital bit stream.
> >
> > DVD+R, DVD-R, DVD+RW,CD+R,CD-R,CD+RW (home recordable types) work on a
> > different principle. When the disk is being written, a laser is used to
> > heat a small spot on the rotating disk. The recording head extends the
> > full radius of the disk. As the spot is heated, the data is recorded at
> > the heated spot by rearranging the magnetic particles on the magnetic
> > reflective coating. The spot instantly cools as the disk spins and the
new
> > magnetic pattern is imprinted in the coating. The magnetic pattern
causes
> > a change in laser beam reflection when played, and the digital
information
> > is detected.
> >
> > A very powerful magnet may be able to change the imprinting on a some
home
> > recordable disks. The laser beam used during recording heats the coating
> > to the Curie point at which the media can easily be imprinted as it
cools.
> > Without heating the coating, the magnetic particles are not easily
> > rearranged.
> >
> > All metal detectors radiate an electro-magnetic field from the coil at
one
> > or more radio frequencies. Because of the long wavelengths and low power
> > involved, a metal detector will not damage any CD or DVD. A hard drive
> > would not be damaged or altered by exposing it to a metal detector
either.
> > The case and circuit design of a hard drive does a good job of shield it
> > from electrical or magnetic damage.
> >
> >
> >
> > "Von Fourche" <[email protected]> wrote in message
> > news:[email protected]...
> >>
> >>
> >> Ok, if I take a powerful magnet and swipe it across a DVD the DVD
will
> >> probably get messed up.
> >>
> >> I just wondering: will a metal detector do the same? If I take my
> >> DFX,
> >> turn it on, and then put a DVD under the coil will the DVD get
> >> erased/screwed up?
> >>
> >> Also, what about computer hard drives? Can a metal detector mess
them
> >> up too?
> >>
> >> Strange questions I know. I'm just wondering!
> >>
> >> Thanks!
> >>
> >>
> >
> >
>
>
