Dear Allison,
   
   You wrote:
> Class 100 is far to dirty for serious chip making.  It's about right
> for sanitary (not sterile) pharmaceutical manufacture (non-paternals).
   
   Hmm. Quoting from <http://dumbo.eeap.cwru.edu/dept/resources/>:
   
> The
> Electronics Design Center incorporates a state of the art
> microfabrication facility for four inch wafer processing which
> includes a class 100 clean room and equipment for the basic processing
             ^^^^^^^^^^^^^^^^^^^^
> steps, diffusion, LPCVD/CVD, photolithography, wet etching, dry
> etching and metalization for the fabrication of microsensors and
> microactuators as well as LSI electronics. It has extensive device
> testing facilities, and advanced workstations for design and modeling.
   
   There is also another facility that may have something to do with this:
   
> The Polymer Microdevice Laboratory is a clean room facility with
> equipment for production of monolayer polymer films and for
> fabrication of semiconductor devices using polymer insulating layers.
   
   The class is not indicated, however.
   
> Lost it to what?  Head crash?  Magnetic field. Mishandeling?
   
   He has never told me, but I assume just from storage. I'm sure that Long
knows how to treat media. When he was managing the CES department's
facilities, everything was just shining: all equipment in excellent
condition, absolutely no dust, all parts neatly stored in antistatic bags,
etc.
   
> Magnetic fields are media damage only.
   
   Yes, and with the ZIP disks in particular, the disk goes too, not just
the data. Iomega has decided to put some recording on them that the drive
requires but cannot produce itself, so degaussing kills a disk.
   
   This brings me to the following question: are the classical DEC disk
packs and other media like this too? For example, according to the 4.3BSD
documentation, RX211 (and RXV21 I assume) cannot format a disk if "the
header information on sector 1, track 0" has been damaged. However, this
apparently doesn't apply to the rest of the disk, so at least the
drive/controller has the ability to write the sector headers itself. The
documentation also says that the density (single or double, FM vs. MFM
really) must be specified for formatting, suggesting that you can change
from one to the other. Also since according to the same doc the track
format is industry standard (IBM 3740 for FM and System 34 for MFM), so if
you have a completely degaussed disk, you should be able to format it on
something less restrictive.
   
   It is also interesting what does the interface between RX drives and
controllers look like. Normally FDDs have the rawest possible interface,
with raw data on the read data and write data lines (each pulse
corresponding to a flux transition). If this case the controller has total
control over the encoding and decides for itself how to go about
formatting. If RXs have such an interface, it should only take a special
controller to make the drive format completely degaussed disks. However,
one thing about DEC RXs makes me doubt that they have such an interface.
Since the distinction between single and double density is nothing more
than FM vs. MFM and the flux transition density is the same, neither the
media nor the drives should care about it, should they? This should be
entirely up to the controller, shouldn't it? Why are RX01 and RX02
different drives then? Also I have heard that both are intrinsically dual,
aren't they? Is it just that two drives are put in the same rackmount box
and connected to the same ribbon cable like FDDs in IBM PCs, or are the two
drives really integrated (share the controller interface logic)? While we
are at it, the story is the same with TU58s, isn't it? The interface
(serial port) is shared by both drives, isn't it? But then how come I hear
that VAX-11/750 has only one TU58 drive and not two like, say, 730? Or is
this incorrect? And how about the RX01 in the 780 console? Is there only
one or are there two?
   
   RMs and RPs seem to be freely formattable, since the 4.3BSD
documentation gives the formatting instructions for all of them and clearly
says that the format procedure actually writes the sector headers. It seems
to imply that the disks are hard-sectored. Is this correct? It would still
be interesting, though, whether there are any servo surfaces that cannot be
written and whether the formatting procedure requires something to be
already on the disk like it does on RX211/RXV21. BTW, what's the difference
between RMs and RPs? Which are removable and which are fixed?
   
   How about RKs? The handy-for-everything 4.3BSD documentation gives
formatting directions for these, so I assume that they are freely
formattable too. Are these hard-sectored or soft-sectored? Do they have
servo? Does the format procedure have any prerequisites? Someone has once
posted which RK disks are removable and which are fixed, but I don't have
that post handy. Do you remember which are which? Just out of curiosity,
what does their controller interface look like? I have been told that RK07s
use the same controller as RK06s, so the interface is the same between
these two, but apparently it is different between RK06 and the earlier
ones.
   
   How about RLs? This time the 4.3BSD documentation has no answer. Are
these formattable? Are they hard-sectored or soft-sectored? You later hint
that they have servo. Is this correct? And what is the difference between
RL01 and RL02? Is RL01 5 MB and RL02 10 MB? I have heard that RL02 can read
RL01 packs, suggesting that the two are mechanically the same. I have also
heard that RL02 packs have two tracks per cylinder. Does this mean that the
pack is actually a single disk? I remember you and others hint that the
controllers are the same for the two, so the interface is the same, right?
Just out of curiosity, what does it (the interface) look like?
   
   How about RAs? I know that RA8x have servo surfaces, but many ST-506/412
and ESDI Winchesters have servo surfaces too, but the data surfaces can be
freely formatted even if they are completely degaussed. Can one format the
data surfaces of an RA8x? How about smaller RAs? How about RA60 packs? Can
they be formatted? Do they have servo?
   
> I've been using RL02s for over 15 years and the newest pack I have is
> about 10 and the reliability is hard to beat.  I've only lost one pack
> and that was to external field munging the servo track.
   
   What's the servo track? I have only heard of servo surfaces, which are
used by the drive to tell the position of the heads at any time. All drives
that don't have a stepper motor to fix the track positions (i.e., all
drives with voice coil head actuators) need servo surfaces, unless they
have embedded servo. But they have to be surfaces, a single track obviously
won't help much with determining the head position at any time.
   
> I know of RK05Fs and RK05s that are old enough to vote.
   
   What's the difference between RK05F and RK05?
   
> I know of a
> RS08 (circa 1968) that is operable, the computer needs work on the core.
   
   What's that?
   
> The only drive that had a bum track record was the RC25.
   
   I have heard the name, but I don't really know anything about it. It
connects through an MSCP controller, doesn't it?
   
   Sincerely,
   Michael Sokolov
   Phone: 440-449-0299
   ARPA Internet SMTP mail: sokolov@alpha.ces.cwru.edu