Re: filmscanners: Best digital archive medium for scans?

["Florian Rist" <florian.rist@stud.tu-muenchen.de>]

Hi Lynn!

> >On a MOD the data is stored by changing the magnetic orientation of a
> >ferro magnetic meterial. This will not fade. To change it very high
> >temperatures and high magnetic fields are needed.
> 
> Cautionary note: I have a (ferro)magnetic tape cast-recording of "Chicago"
> that somehow got too close to a degausing agent (probably a radio
> speaker). All the tape that was exposed (that part between one roller and
> the next, not covered by plastic) is missing any resemblence to music.
> Fortunately, I can sing, hum, or whistle my way through "Chicago" to cover
> the lost music--but I somehow doubt that I could do the same with lost
> photo-data.
> 
> Any questions?

Well, you cant compare the to media. It's true both use magnetic effects to 
store information, but to somewhat different physical effects are uses.

I case of the audio the tape recording (or floppy disks) small iron particles 
are embedded in a non ferromagnetic material. During a recording these 
ferromagnetic particles are magnetised and the information is stored by 
modulating the strength of magnetism. The problem is even a relatively low 
magnetic field can change the this and harm, destroy the data.


On a MO(D) media information is stored in a different way: The information is 
stored by changing the magnetic polarisation of a media, not by modulating the 
strength of a magnetic field. To change the magnetic polarisation of a pooper 
media you'll either need extremely strong magnetic fields (no 
change to reach them by using anything your can usually find at home) or very 
high temperatures above to the Curie temperature of the material (a few hundred 
degrees Celsius).

Information is written to the MO media by applying a strong magnetic field and 
heating up a small area on the disk by using a strong laser beam. A small 
amount of material heats up, the magnetic orientation changes, as the material 
cools down and the magnetic polarisation "freezes". To read out 
the information again a low energetic laser is used. There are special 
materials that change there optical specification according to there magnetic 
polarisation.


So, the info is save on MO media, but not on your audio tape. :-)


I hope my poor English is good enough to explain these things. Unfortunately my 
knowledge of the physics behind it isn't very good either. I uses to know these 
things, when I was studying math and physics a few years back. No that I 
changed to architecture I tend to forget these things ...

cu
Flo


PS: Hey, isnt any one interested into my nice Maxoptix SCSI MOD T5-2600?