Parallel port hard drives?

From: Richard Erlacher <edick_at_idcomm.com>
Date: Tue Mar 28 09:07:29 2000

Please see embedded comments below.

Dick

----- Original Message -----
From: Pete Turnbull <pete_at_dunnington.u-net.com>
To: <classiccmp_at_classiccmp.org>
Sent: Tuesday, March 28, 2000 1:36 AM
Subject: Re: Parallel port hard drives?


> On Mar 27, 18:44, Richard Erlacher wrote:
>
> > ----- Original Message -----
> > From: Pete Turnbull <pete_at_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?
It
> > 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
my
> > > 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
> being
> > 96TPI-certified, "QD" presumably for quad density, since you get twice
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
same
> > > > 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
disks
> 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
fine
> -- and I suspect that's just the result of better quality control.
>
> --
>
> Pete Peter Turnbull
> Dept. of Computer Science
> University of York
Received on Tue Mar 28 2000 - 09:07:29 BST

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