28 Mar
2000
28 Mar
'00
1:07 a.m.
Please see embedded comments below.
Dick
----- Original Message -----
From: Pete Turnbull <pete(a)dunnington.u-net.com>
To: <classiccmp(a)classiccmp.org>
Sent: Tuesday, March 28, 2000 1:36 AM
Subject: Re: Parallel port hard drives?
my
being
> 96TPI-certified, "QD" presumably for quad density, since you get twice
as
same
disks
fine
On Mar 27, 18:44, Richard Erlacher wrote:
It
----- Original Message -----
From: Pete Turnbull <pete(a)dunnington.u-net.com>
> On Mar 27, 19:57, Tony Duell wrote:
> > fact behaves like the second type above
-- a 98tpi (80 cylinder)
drive
Surely you mean 96 tpi . . . right?
I'm sure that was just a typo on Tony's part :-)
> I'm curious ... How do you "set" a
> 1.2MB drive to behave as a 720-K drive, i.e. use that type of medium? > seems to me that, at a minimum, the controller
would have to be
seriously
involved as
well.
Assuming the HD drive is correctly jumpered, you simply get the controller
to put a low signal on pin 2 (density) of the interface. On most drives,
that will also change the speed from 360 rpm to 300; on others, not.
> > Furthermore, the media used in 96 tpi standard density disks is, in > > experience, the same as that used in 48 tpi
standard density disks.
It
> even says
so in my CDC drive manuals. However, as we all (ought to)
know,
the media
for HD disks is very different.
The fact remains that there are diskettes specifically designated as many tracks as
with a double density diskette, which were, originally
sold
at a higher price than the "360K"
Indeed, and I have lots like that, ie either "certified for 96 tpi" or in
a few cases, "QD". However, the differential is partly marketing, and
partly because manufacturers often tested 96 tpi disks more carefully for
microscopic blemishes -- a tiny defect might cause a disk to be rejected
for 96 tpi, but pass a test for 48 tpi. Many (most?) manufacturers used
exactly the same media/emulsion for both types -- I know for a fact that
Dysan and Verbatim did, although I also know that Dysan at one time made
disks that looked slightly different, and presumably those did use a
slighlty different coating.
> > > According to all the data I can find (which is not much), the centre
> > lines
> > > of the 48tpi tracks and the centre lines of alternate 96tpi tracks
> > > coincide. This means (amongst other things) that you can use the
> > > alignment disk for both types of
drive.
> >
> This would follow but for the technique used for writing radial
alignment
tracks.
I don't follow -- the instructions for my Shugart and Dysan alignment clearly state that the disk is suitable for both 96
tpi and 48 tpi drives,
and lists the apropriate track numbers for the various tests, such as the
cats-eyes alignment test (and, yes, the track number for 96 tpi is simply
double the number for 48 tpi in each case).
I had the sense that the runout with which the alignment diskettes for 48TPI
are written would exceed half the track width of a 96TPI diskette. Perhaps
that;s not the case. I've never had occasion to do radial alignment checks
on a 5-1'4" drive. The margin for 8" drives, however, seems to be quite
substantial, hency my belief that the angualr displacement to provide a
significant error would be more than half what's seen of a half-track drive.
results I had and observed in others' lack of
success certainly support
the
belief that the media were not the same.
Perhaps you've been unlucky. I too have found some old 48 tpi media are
just not good enough, giving one or two errors, but most post 1980 are -- and I suspect that's just the result of better
quality control.
--
Pete Peter Turnbull
Dept. of Computer Science
University of York