🚀 go-pugleaf

A few words regarding the magneto-optical disk introduced in the NeXT
computer:

If the disk is similar to the type I researched in the spring (and I believe
it is), it is not a combination winchester/WORM disk--rather it is a device
which is read from and written to with a laser. But instead of scoring a
hole in the reflective coating, the laser records a polarization change in
the disk when it heats the alloy above its curie temperature.  When a
magnetic field is present, the bit retains its magnetic orientation after
the spot cools, and the bit can be read by reflecting the same beam (at low
power) from the disk and detecting the phase change of the beam reflected
from the magnetized bit (Farraday effect, it's called).

Since we're dealing with laser optics there's a much higher information
density than magnetic disks (at least in theory).  The articles I read
seemed to indicate a maximum capacity of around a gigabyte for a 5-1/4"
disk.

The main drawback is speed, and first generation drives are probably in
the 50 to 100 ms range (but this is just a guess on my part).  There's no
reason that the drive can't be as fast as a winchester but technology of
the disks and drives will probably have to be improved to support it.
There's comparable number of write/erase cycles and bit error rates (BER)
as with a winchester.

If the NeXT can demonstrate a working erasable M/O (magneto-optic) disk then
we'll probably start seeing them in a few months for other computers, and
most likely with SCSI or ESDI controllers.  I for one would be interested in
having a few hundred megabytes of removable erasable storage available, even
if it is a little bit pokey.