mjkobb@mit-amt.MEDIA.MIT.EDU (Michael J Kobb) (10/12/89)
Hello. A friend of mine and I have been having a rather large argument regarding how erasable optical (EO) drives work. I maintain that the disk is written to by heating the desired spot with the laser, then using the magnetic head to set the field on that spot so that it's either a 1 or 0. Reading, I maintain, is done much the same way, by heating the desired spot, and reading the field off of it with the magnetic head (both of these presuppose that the magnetic characteristics of the medium are altered by the heat, so that a relatively large head will really only act on the heated spot. My friend maintains that the drive is written to with the laser and the magnet, but that it is read exclusively with the laser, depending on the altered magnetic field of the molecules to either reflect or scatter the laser beam. Question: which, if either, of us is correct? Could some kind soul point me to a reference where I can get a complete description (MacWorld or MacUser references would be preferred, since I have access to archives of them. Or, if someone would like to tell me where there's an online archive with this info, and how I access it, that would be fine, too.)? Thanks in advance. --Mike
mjkobb@mit-amt.MEDIA.MIT.EDU (Michael J Kobb) (10/12/89)
Well, this is a new one... I've never responded to one of my own posts before.
I've received responses that said, in four words or less "your friend is right"
(The original question was whether the erasable optical drives read
magnetically w/the help of a laser, or if it's strict laser. My friend
maintained that it was strict laser, which is apparently correct.)
Okay, so next question. On the news the other morning, I heard that Sony had
announced that they will soon (?) be marketing a CD recorder that would have
>10 million rewrite capability, and would be compatible with existing CD's for
playback (though you'd need special disks to record). Okay, so does anyone
have any further info on this? What technology do they use? NeXT disks appear
to be hard-sectored, but CD's aren't. Other than this difference, could they
conceivably be read by the same technology (in other words, could a drive using
EO technology write to a soft-sectored disk in a way that could be read by
a normal disc player)? Otherwise what did they do? Also, they claimed that
price would be comparable to a normal CD player, which I read as meaning
<$700 at most. How is this possible considering the expense of EO drives.
Finally, if they're using a different technology, could Sony market it as an
inexpensive alternative to current EO (of which they are apparently a prime
manufacturer)?
Aigh!!!!
Thanks in advance for any info. If you have a really definitive answer, go
on and post it. Otherwise, email me and I'll summarize...
--Mikedorourke@polyslo.CalPoly.EDU (David M. O'Rourke) (10/12/89)
mjkobb@media-lab.media.mit.edu (Michael J Kobb) writes: > My friend maintains that the drive is written to with the laser and the >magnet, but that it is read exclusively with the laser, depending on the >altered magnetic field of the molecules to either reflect or scatter the laser >beam. > > Question: which, if either, of us is correct? I'm no expert on this subject, but my file structures teacher did have us read a very interesting article on the subject. It's my understanding that the poster's description of how the disk is written to is essentially correct. The disk is read by bouncing a laser off of one of the "bit's" on the disk, and depending on how that "bit" was polarized you can read the effect on the laser. It seems that you can read how a laser is polarized, and the magnetic field in the bit area will affect the laser's polarization, which is read, and therefore you can encode 0's & 1's on the different polarizations. Hope this helps, I'm sure if I'm wrong people will notify the net :-) -- \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\|///////////////////////////////////////// David M. O'Rourke____________________|_____________dorourke@polyslo.calpoly.edu | Graduating in March of 1990, with a BS in Computer Science & need a Job. | |_____________________________________________________________________________|