cb2o+@andrew.cmu.edu (Charles Edward Batey, Jr.) (10/15/88)
As I understand it, the operation of the NeXT optical drive is as follows: First, the disc used in the drive is different than a normal optical disc, or CD. It uses the same plastic coating as a standard CD, however, the core of the disc is made of aluminum coated with some magnetic material. Second, the laser in the drive operates at two intensities. When writing, the high-intensity laser is used to heat the magnetic material up to the Curie point (where the current magnetic polarization of the material can be affected by a Magnetic field). Then a magnetic field is applied at that point on the disc, thus altering the magnetic polarization. There are two orientations of the magnetic field - one represents a zero and the other a one. Accordingly, there are two possible polarized states the magnetic material can have. When reading, the drive uses the low-intensity laser setting and reads the disc by reflecting the laser off the disc, through a polarizer, and into an analyzer that determines the intensity of the beam. It seems that the beam, when refracted through the material and reflected off of the aluminum core, has a distinct direction of polarization, one for each of the two states of the material. Thus by passing the beam through a polarizing filter, the differing intensities of the resulting light represent either a one or a zero. Also, when writing to the disc, it uses a three pass system. Once to set all of the bits needed in storing the information to zero (the erase pass), a second time to set all of the one bits, and a third time to verify the code. Hope this helps. Ted Batey Carnegie Mellon University Pittsburgh, PA
shap@polya.Stanford.EDU (Jonathan S. Shapiro) (10/16/88)
Can anyone present a cogent theory as to why they elected to go with a CD disk over standard magnetic media. It would seem to me, for example, that using a Wren IV or any of a number of other drives would almost undoubtedly be considerably cheaper than the laser drive, though I grant that it would introduce the need for backup and distribution media. What benefit to the laser drive, then? Also, consider the following problem: MicroSoft (strictly hypothetical) decides they want to distribute MS Word to me. What media does it come on? How expensive is the media? How can I be sure that the files I need on my original disk are accessable from the MS disk. Alternatively, how do I copy MS Word onto my drive? Jon
caromero@phoenix.Princeton.EDU (C. Antonio Romero) (10/17/88)
In article <4489@polya.Stanford.EDU> shap@polya.Stanford.EDU (Jonathan S. Shapiro) writes: >Can anyone present a cogent theory as to why they elected to go with a >CD disk over standard magnetic media. It would seem to me, for >example, that using a Wren IV or any of a number of other drives would >almost undoubtedly be considerably cheaper than the laser drive, Well, for one thing, it's in character for Steve Jobs to try to do things differently. Witness the Mac's disks-- not quite unique at the time, but damn close. Optical drives are the coming thing, so Steve had to throw one in. For another thing, do drives like the Wren IV have removable platters? Can they offer the same capacity at the same price per blank disk (something like $50 each...)? I'll believe a cheaper magnetic drive with a fixed disk, but removable... that sounds a little optimistic. Followups to comp.misc. -Antonio Romero romero@confidence.princeton.edu
dorourke@polyslo.CalPoly.EDU (David M. O'Rourke) (10/18/88)
In article <4489@polya.Stanford.EDU> shap@polya.Stanford.EDU (Jonathan S. Shapiro) writes: >What benefit to the laser drive, then? Removable Capacity!! Do you know of any cheap drives that offer a protable 256 MegaBytes, in a very reliable format. This is a machine for University Lab enviroments. Wouldn't it be nice as a student to be able to bring up your very own Unix enviroment regardless of what machine you were on. :-) >Also, consider the following problem: MicroSoft (strictly MicroSoft has already stated that they will not be developing any SW for the next Machine. Given the popularity of OS/2, I think this might be a bad idea. But who am I, just someone who hates MS. :-) -- David M. O'Rourke dorourke@polyslo.calpoly.edu "If it doesn't do Windows, then it's not a computer!!!" Disclaimer: I don't represent the school. All opinions are mine!